In Slave Lake in particular, which vies in dimensions with some of the

great fresh-water seas of Canada, the quantity of drift-timber brought

down annually is enormous. "As the trees," says Dr. Richardson, "retain

their roots, which are often loaded with earth and stones, they readily

sink, especially when water-soaked; and, accumulating in the eddies,

form shoals, which ultimately augment into islands. A thicket of small

willows covers the new-formed island as soon as it appears above water,

and their fibrous roots serve to bind the whole firmly together.

Sections of these islands are annually made by the river, assisted by

the frost; and it is interesting to study the diversity of appearances

they present, according to their different ages. The trunks of the trees

gradually decay until they are converted into a blackish brown substance

resembling peat, but which still retains more or less of the fibrous

structure of the wood; and layers of this often alternate with layers of

clay and sand, the whole being penetrated, to the depth of four or five

yards or more, by the long fibrous roots of the willows. A deposition of

this kind, with the aid of a little infiltration of bituminous matter,

would produce an excellent imitation of coal, with vegetable impressions

of the willow-roots. What appeared most remarkable was the horizontal

slaty structure that the old alluvial banks presented, or the _regular

curve_ that the strata assumed from unequal subsidence.

"It was in the rivers only that we could observe sections of these

deposits; but the same operation goes on, on a much more magnificent

scale, in the lakes. A shoal of many miles in extent is formed on the

south side of Athabasca Lake, by the drift-timber and vegetable debris

brought down by the Elk River; and the Slave Lake itself must in process

of time be filled up by matters daily conveyed into it from Slave River.

Vast quantities of drift-timber are buried under the sand at the mouth

of the river, and enormous piles of it are accumulated on the shores of

every part of the lake."[1062]

The banks of the Mackenzie display almost everywhere horizontal beds of

wood coal, alternating with bituminous clay, gravel, sand, and friable

sandstone; sections, in short, of such deposits as are now evidently

forming at the bottom of the lakes which it traverses.

Notwithstanding the vast forests intercepted by the lakes, a still

greater mass of drift-wood is found where the Mackenzie reaches the sea,

in a latitude where no wood grows at present except a few stunted

willows. At the mouths of the river the alluvial matter has formed a

barrier of islands and shoals, where we may expect a great formation of

coal at some distant period.

The abundance of floating timber on the Mackenzie is owing, as Dr.

Richardson informs me, to the direction and to the length of the course

of this river, which runs from south to north, so that the sources of

the stream lie in much warmer latitudes than its mouths. In the country,

therefore, where the sources are situated, the frost breaks up at an

earlier season, while yet the waters in the lower part of its course are

ice-bound. Hence the current of water, rushing down northward, reaches a

point where the thaw has not begun, and, finding the channel of the

river blocked up with ice, it overflows the banks, sweeping through

forests of pines, and carrying away thousands of uprooted trees.

_Drift-timber on coasts of Iceland, Spitzbergen, &c._--The ancient

forests of Iceland, observes Malte-Brun, have been improvidently

exhausted; but, although the Icelander can obtain no timber from the

land, he is supplied with it abundantly by the ocean. An immense

quantity of thick trunks of pines, firs, and other trees, are thrown

upon the northern coast of the island, especially upon the North Cape

and Cape Langaness, and are then carried by the waves along these two

promontories to other parts of the coast, so as to afford sufficiency of

wood for fuel and for constructing boats. Timber is also carried to the

shores of Labrador and Greenland; and Crantz assures us that the masses

of floating wood thrown by the waves upon the island of John de Mayen

often equal the whole of that island in extent.[1063]

In a similar manner the bays of Spitzbergen are filled with drift-wood,

which accumulates also upon those parts of the coast of Siberia that are

exposed to the east, consisting of larch trees, pines, Siberian cedars,

firs, and Pernambuco and Campeachy woods. These trunks appear to have

been swept away by the great rivers of Asia and America. Some of them

are brought from the Gulf of Mexico by the Bahama stream; while others

are hurried forward by the current which, to the north of Siberia,

constantly sets in from east to west. Some of these trees have been

deprived of their bark by friction, but are in such a state of

preservation as to form excellent building timber.[1064] Parts of the

branches and almost all the roots remain fixed to the pines which have

been drifted into the North Sea, into latitudes too cold for the growth

of such timber, but the trunks are usually barked.

The leaves and lighter parts of plants are seldom carried out to sea, in

any part of the globe, except during tropical hurricanes among islands,

and during the agitations of the atmosphere which sometimes accompany

earthquakes and volcanic eruptions.

_Comparative number of living and fossilized species of plants._--It

will appear from these observations that, although the remains of

terrestrial vegetation, borne down by aqueous causes from the land, are

chiefly deposited at the bottom of lakes or at the mouths of rivers, yet

a considerable quantity is drifted about in all directions by currents,

and may become imbedded in any _marine_ formation, or may sink down,

when water-logged, to the bottom of unfathomable abysses, and there

accumulate without intermixture with other substances.

It may be asked whether we have any data for inferring that the remains

of a considerable proportion of the existing species of plants will be

permanently preserved, so as to be hereafter recognizable, supposing the

strata now in progress to be at some future period upraised? To this

inquiry it may be answered, that there are no reasons for expecting that

more than a small number of the plants now flourishing in the globe will

become fossilized; since the entire habitations of a great number of

them are remote from lakes and seas, and even where they grow near to

large bodies of water, the circumstances are quite accidental and

partial which favor the imbedding and conservation of vegetable

remains. Suppose, for example, that the species of plants inhabiting the

hydrographical basin of the Rhine, or that region, extending from the

Alps to the sea, which is watered by the Rhine and its numerous

tributaries, to be about 2500 in number, exclusive of the cryptogamic

class. This estimate is by no means exaggerated; yet if a geologist

could explore the deposits which have resulted from the sediment of the

Rhine in the Lake of Constance, and off the coast of Holland, he could

scarcely expect to obtain from the recent strata the leaves, wood, and

seeds of _fifty_ species in such a state of preservation as to enable a

botanist to determine their specific characters with certainty.

Those naturalists, therefore, who infer that the ancient flora of the

globe was, at certain periods, less varied than now, merely because they

have as yet discovered only a few hundred fossil species of a particular

epoch, while they can enumerate more than one hundred thousand living

ones, are reasoning on a false basis, and their standard of comparison

is not the same in the two cases.

_Submarine forests on coast of Hants._--We have already seen that the

submarine position of several forests, or the remains of trees standing

in a vertical position on the British shores, has been due, in some

instances, to the subsidence of land.[1065] There are some cases which

require a different explanation. My friend, Mr. Charles Harris,

discovered, in 1831, evident traces of a fir-wood beneath the mean level

of the sea, at Bournmouth, in Hampshire, the formation having been laid

open during a low spring tide. It is composed of peat and wood, and is

situated between the beach and a bar of sand about 200 yards off, and

extends fifty yards along the shore. It also lies in the direct line of

the Bournmouth Valley, from the termination of which it is separated by

200 yards of shingle and drift-sand. Down the valley flows a large

brook, traversing near its mouth a considerable tract of rough, boggy,

and heathy ground, which produces a few birch-trees, and a great

abundance of the _Myrica gale_. Seventy-six rings of annual growth were

counted in a transverse section of one of the buried fir-trees, which

was fourteen inches in diameter. Besides the stumps and roots of fir,

pieces of alder and birch are found in the peat; and it is a curious

fact, that a part of many of the trees have been converted into iron

pyrites. The peat rests on pebbly strata, precisely similar to the sand

and pebbles occurring on the adjoining heaths.

As the sea is encroaching on this shore, we may suppose that at some

former period the Bourne Valley extended farther, and that its extremity

consisted, as at present, of boggy ground, partly clothed with

fir-trees. The bog rested on that bed of pebbles which we now see below

the peat; and the sea, in its progressive encroachments, eventually laid

bare, at low water, the sandy foundations; upon which a stream of fresh

water, rushing through the sand at the fall of the tides, carried out

loose sand with it. The superstratum of vegetable matter, being matted

and bound together by the roots of trees, remained; but being

undermined, sank down below the level of the sea, and then the waves

washed sand and shingle over it. In support of this hypothesis, it may

be observed, that small streams of fresh water often pass under the

sands of the sea-beach, so that they may be crossed dry-shod; and the

water is seen, at the point where it issues, to carry out sand and even

pebbles.

_Mineralization of plants_--Although the botanist and chemist have as yet

been unable to explain fully the manner in which wood becomes petrified,

it is nevertheless ascertained that, under favorable circumstances, the

lapidifying process is now continually going on. A piece of wood was

lately procured by Mr. Stokes, from an ancient Roman aqueduct in

Westphalia, in which some portions were converted into spindle-shaped

bodies, consisting of carbonate of lime, while the rest of the wood

remained in a comparatively unchanged state.[1066] It appears that in

some cases the most perishable, in others the most durable, portions of

plants are preserved, variations which doubtless depend on the time when

the mineral matter was supplied. If introduced immediately, on the first

commencement of decomposition, then the most destructible parts are

lapidified, while the more durable do not waste away till afterwards,

when the supply has failed, and so never become petrified. The converse

of these circumstances gives rise to exactly opposite results.

Professor Goppert, of Breslau, has instituted a series of curious

experiments, in which he has succeeded in producing some very remarkable

imitations of fossil petrifactions. He placed recent ferns between soft

layers of clay, dried these in the shade, and then slowly and gradually

heated them, till they were red-hot. The result was the production of so

perfect a counterpart of fossil plants as might have deceived an

experienced geologist. According to the different degrees of heat

applied, the plants were obtained in a brown or perfectly carbonized

condition; and sometimes, but more rarely, they were in a black shining

state, adhering closely to the layer of clay. If the red heat was

sustained until all the organic matter was burnt up, only an impression

of the plant remained.

The same chemist steeped plants in a moderately strong solution of

sulphate of iron, and left them immersed in it for several days, until

they were thoroughly soaked in the liquid. They were then dried, and

kept heated until they would no longer shrink in volume, and until every

trace of organic matter had disappeared. On cooling them he found that

the oxide formed by this process had taken the form of the plants. A

variety of other experiments were made by steeping animal and vegetable

substances in siliceous, calcareous, and metallic solutions, and all

tended to prove that the mineralization of organic bodies can be carried

much farther in a short time than had been previously supposed.[1067]

_Imbedding of the Remains of Insects._

I have observed the elytra and other parts of beetles in a band of

fissile clay, separating two beds of recent shell-marl, in the Loch of

Kinnordy in Forfarshire. Amongst these, Mr. Curtis recognized _Elator

lincatus_ and _Atopa cervina_, species still living in Scotland. These,

as well as other remains which accompanied them, appear to belong to

terrestrial, not aquatic species, and must have been carried down in

muddy water during an inundation. In the lacustrine peat of the same

locality, the elytra of beetles are not uncommon; but in the deposits of

drained lakes generally, and in the silt of our estuaries, the relics of

this class of the animal kingdom are rare. In the blue clay of very

modern origin of Lewes levels, Dr. Mantell has found the Indusia, or

cases of the larvae of Phryganea, in abundance, with minute shells

belonging to the genera Planorbis, Limnea, &c., adhering to them.[1068]

When speaking of the migrations of insects, I pointed out that an

immense number are floated into lakes and seas by rivers, or blown by

winds far from the land; but they are so buoyant that we can only

suppose them, under very peculiar circumstances, to sink to the bottom

before they are either devoured by insectivorous animals or decomposed.

_Remains of Reptiles._

As the bodies of several crocodiles were found in the mud brought down

to the sea by the river inundation which attended an earthquake in Java,

in the year 1699, we may imagine that extraordinary floods of mud may

stifle many individuals of the shoals of alligators and other reptiles

which frequent lakes and the deltas of rivers in tropical climates.

Thousands of frogs were found leaping about among the wreck, carried

into the sea by the inundations in Morayshire, in 1829;[1069] and it is

evident that whenever a sea-cliff is undermined, or land is swept by

other violent causes into the sea, land reptiles may be carried in.

_Remains of Birds._

We might have anticipated that the imbedding of the remains of birds in

new strata would be of very rare occurrence; for their powers of flight

insure them against perishing, by numerous casualties to which

quadrupeds are exposed during floods; and if they chance to be drowned,

or to die when swimming on the water, it will scarcely ever happen that

they will be submerged so as to become preserved in sedimentary

deposits. In consequence of the hollow tubular structure of their bones

and the quantity of their feathers, they are extremely light in

proportion to their volume; so that when first killed they do not sink

to the bottom like quadrupeds, but float on the surface until the

carcass either rots away or is devoured by predaceous animals. To these

causes we may ascribe the absence of any vestige of the bones of birds

in the recent marl formations of Scotland; although these lakes, until

the moment when they were artificially drained, were frequented by a

great abundance of waterfowl.

_Imbedding of Terrestrial Quadrupeds._

River inundations recur in most climates at very irregular intervals,

and expend their fury on those rich alluvial plains where herds of

herbivorous quadrupeds congregate together. These animals are often

surprised; and, being unable to stem the current, are hurried along

until they are drowned, when they sink at first immediately to the

bottom. Here their bodies are drifted along, together with sediment,

into lakes or seas, and may then be covered by a mass of mud, sand, and

pebbles, thrown down upon them. If there be no sediment superimposed,

the gases generated by putrefaction usually cause the bodies to rise

again to the surface about the ninth, or at latest the fourteenth day.

The pressure of a thin covering of mud would not be sufficient to retain

them at the bottom; for we see the putrid carcasses of dogs and cats,

even in rivers, floating with considerable weights attached to them, and

in sea-water they would be still more buoyant.

Where the body is so buried in drift sand, or mud accumulated upon it,

as never to rise again, the skeleton may be preserved entire; but if it

comes again to the surface while in the process of putrefaction, the

bones commonly fall piecemeal from the floating carcass, and may in that

case be scattered at random over the bottom of the lake, estuary, or

sea; so that a jaw may afterwards be found in one place, a rib in

another, a humerus in a third--all included, perhaps, in a matrix of

fine materials, where there may be evidence of slight transporting power

in the current, or even of none, but simply of some chemical

precipitate.

A large number of the bodies of drowned animals, if they float into the

sea or a lake, especially in hot climates, are instantly devoured by

sharks, alligators, and other carnivorous beasts, which may have power

to digest even the bones; but during extraordinary floods, when the

greatest number of land animals are destroyed, the waters are commonly

so turbid, especially at the bottom of the channel, that even aquatic

species are compelled to escape into some retreat where there is clearer

water, lest they should be stifled. For this reason, as well as the

rapidity of sedimentary deposition at such seasons, the probability of

carcasses becoming permanently imbedded is considerable.

_Flood in the Solway Firth, 1794._--One of the most memorable floods of

modern date, in our island, is that which visited part of the southern

borders of Scotland, on the 24th of January, 1794, and which spread

particular devastation over the country adjoining the Solway Firth.

We learn from the account of Captain Napier, that the heavy rains had

swollen every stream which entered the Firth of Solway; so that the

inundation not only carried away a great number of cattle and sheep, but

many of the herdsmen and shepherds, washing down their bodies into the

estuary. After the storm, when the flood subsided, an extraordinary

spectacle was seen on a large sand-bank called "the beds of Esk," where

there is a meeting of the tidal waters, and where heavy bodies are

usually left stranded after great floods. On this single bank were found

collected together the bodies of 9 black cattle, 3 horses, 1840 sheep,

45 dogs, 180 hares, besides a great number of smaller animals, and,

mingled with the rest, the corpses of two men and one woman.[1070]

_Floods in Scotland, 1829._--In those more recent floods in Scotland, in

August, 1829, whereby a fertile district on the east coast became a

scene of dreadful desolation, a vast number of animals and plants were

washed from the land, and found scattered about after the storm, around

the mouths of the principal rivers. An eye-witness thus describes the

scene which presented itself at the mouth of the Spey, in

Morayshire:--"For several miles along the beach crowds were employed in

endeavoring to save the wood and other wreck with which the

heavy-rolling tide was loaded; whilst the margin of the sea was strewed

with the carcasses of domestic animals, and with millions of dead hares

and rabbits."[1071]

_Savannahs of South America._--We are informed by Humboldt, that during

the periodical swellings of the large rivers in South America great

numbers of quadrupeds are annually drowned. Of the wild horses, for

example, which graze in immense troops in the savannahs, thousands are

said to perish when the river Apure, a tributary of the Orinoco, is

swollen, before they have time to reach the rising ground of the Llanos.

The mares, during the season of high water, may be seen, followed by

their colts, swimming about and feeding on the grass, of which the top

alone waves above the waters. In this state they are pursued by

crocodiles; and their thighs frequently bear the prints of the teeth of

these carnivorous reptiles. "Such is the pliability," observes the

celebrated traveller, "of the organization of the animals which man has

subjected to his sway, that horses, cows, and other species of European

origin, lead, for a time, an amphibious life, surrounded by crocodiles,

water-serpents, and manatees. When the rivers return again into their

beds, they roam in the savannah, which is then spread over with a fine

odoriferous grass, and enjoy, as in their native climate, the renewed

vegetation of spring."[1072]

_Floods of the Parana._--The great number of animals which are drowned

in seasons of drought in the tributaries of the Plata, was before

mentioned. Sir W. Parish states, that the Parana, flowing from the

mountains of Brazil to the estuary of the Plata, is liable to great

floods, and during one of these, in the year 1812, vast quantities of

cattle were carried away, "and when the waters began to subside, and the

islands which they had covered became again visible, the whole

atmosphere for a time was poisoned by the effluvia from the innumerable

carcasses of skunks, capybaras, tigers, and other wild beasts which had

been drowned."[1073]

_Floods of the Ganges._--We find it continually stated, by those who

describe the Ganges and Burrampooter, that these rivers carry before

them, during the flood season, not only floats of reeds and timber, but

dead bodies of men, deer, and oxen.[1074]

_In Java, 1699._--I have already referred to the effects of a flood

which attended an earthquake in Java in 1699, when the turbid waters of

the Batavian river destroyed all the fish except the carp; and when

drowned buffaloes, tigers, rhinoceroses, deer, apes, and other wild

beasts, were brought down to the sea-coast by the current, with several

crocodiles which had been stifled in the mud. (See above, p. 503.)

On the western side of the same island, in the territory of Galongoon,

in the Regencies, a more recent volcanic eruption (that of 1822, before

described) (see above, p. 431) was attended by a flood, during which the

river Tandoi bore down hundreds of carcasses of rhinoceroses and

buffaloes, and swept away more than one hundred men and women from a

multitude assembled on its banks to celebrate a festival. Whether the

bodies reached the sea, or were deposited, with drift matter, in some

large intervening alluvial plains, we are not informed.[1075]

_Sumatra._--"On the coast of Orissa," says Heynes, "I have seen tigers

and whole herds of black cattle carried along by what are called

freshes, and trees of immense size."[1076]

_In Virginia, 1771._--I might enumerate a great number of local deluges

that have swept through the fertile lands bordering on large rivers,

especially in tropical countries, but I should surpass the limits

assigned to this work. I may observe, however, that the destruction of

the islands, in rivers, is often attended with great loss of lives. Thus

when the principal river in Virginia rose, in 1771, to the height of

twenty-five feet above its ordinary level, it swept entirely away Elk

Island, on which were seven hundred head of quadrupeds,--horses, oxen,

sheep, and hogs,--and nearly one hundred houses.[1077]

The reader will gather, from what was before said respecting the

deposition of sediment by aqueous causes, that the greater number of the

remains of quadrupeds drifted away by rivers must be intercepted by

lakes before they reach the sea, or buried in freshwater formations near

the mouths of rivers. If they are carried still farther, the

probabilities are increased of their rising to the surface in a state of

putrefaction, and, in that case, of being there devoured by aquatic

beasts of prey, or of subsiding into some spots whither no sediment is

conveyed, and, consequently, where every vestige of them will, in the

course of time, disappear.

_Skeletons of animals in recent shell-marl, Scotland._--In some

instances, the skeletons of quadrupeds are met with abundantly in recent

shell-marls in Scotland, where we cannot suppose them to have been

imbedded by the action of rivers or floods. They all belong to species

which now inhabit, or are known to have been indigenous in Scotland. The

remains of several hundred skeletons have been procured within the last

century from five or six small lakes in Forfarshire, where shell-marl

has been worked. Those of the stag (_Cervus Elaphas_) are most numerous;

and if the others be arranged in the order of their relative abundance,

they will nearly follow thus--the ox, the boar, the horse, the sheep,

the dog, the hare, the fox, the wolf, and the cat. The beaver seems

extremely rare; but it has been found in the shell-marl of Loch Marlie,

in Perthshire, and in the parish of Edrom, in Berwickshire.

In the greater part of these lake-deposits there are no signs of floods;

and the expanse of water was originally so confined, that the smallest

of the above-mentioned quadrupeds could have crossed, by swimming from

one shore to the other. Deer, and such species as take readily to the

water, may often have been mired in trying to land, where the bottom was

soft and quaggy, and in their efforts to escape may have plunged deeper

into the marly bottom. Some individuals, I suspect, of different

species, have fallen in when crossing the frozen surface in winter; for

nothing can be more treacherous than the ice when covered with snow, in

consequence of the springs, which are numerous, and which, retaining

always an equal temperature, cause the ice, in certain spots, to be

extremely thin, while in every other part of the lake it is strong

enough to bear the heaviest weights.

_Mammiferous remains in marine strata._--As the bones of mammalia are

often so abundantly preserved in peat, and such lakes as have just been

described, the encroachments of a sea upon a coast may sometimes throw

down the imbedded skeletons, so that they may be carried away by tides

and currents, and entombed in submarine formations. Some of the smaller

quadrupeds, also, which burrow in the ground, as well as reptiles and

every species of plant, are liable to be cast down into the waves by

this cause, which must not be overlooked, although probably of

comparatively small importance amongst the numerous agents whereby

terrestrial organic remains are included in submarine strata.

During the great earthquake of Conception in 1835, some cattle, which

were standing on the steep sides of the island of Quiriquina, were

rolled by the shock into the sea, while on a low island at the head of

the Bay of Conception seventy animals were washed off by a great wave

and drowned.[1078]

CHAPTER XLVIII.

IMBEDDING OF THE REMAINS OF MAN AND HIS WORKS IN SUBAQUEOUS STRATA.

Drifting of human bodies to the sea by river

inundations--Destruction of bridges and houses--Loss of lives by

shipwreck--How human corpses may be preserved in recent

deposits--Number of wrecked vessels--Fossil skeletons of men--Fossil

canoes, ships, and works of art--Chemical changes which metallic

articles have undergone after long submergence--Imbedding of cities

and forests in subaqueous strata by subsidence--Earthquake of Cutch

in 1819--Buried Temples of Cashmere--Berkeley's arguments for the

recent date of the creation of man--Concluding remarks.

I shall now proceed to inquire in what manner the mortal remains of man

and the works of his hands may be permanently preserved in subaqueous

strata. Of the many hundred million human beings which perish in the

course of every century on the land, every vestige is usually destroyed

in the course of a few thousand years; but of the smaller number that

perish in the waters, a certain proportion must be entombed under

circumstances that may enable parts of them to endure throughout entire

geological epochs.

The bodies of men, together with those of the inferior animals, are

occasionally washed down during river inundations into seas and lakes.

(See pp. 726-728.) Belzoni witnessed a flood on the Nile in September,

1818, where, although the river rose only three feet and a half above

its ordinary level, several villages, with some hundreds of men, women,

and children, were swept away.[1079] It was before mentioned that a rise

of six feet of water in the Ganges, in 1763, was attended with a much

greater loss of lives. (See above, p. 278.)

In the year 1771, when the inundations in the north of England appear to

have equalled the floods of Morayshire in 1829, a great number of houses

and their inhabitants were swept away by the rivers Tyne, Can, Wear,

Tees, and Greta; and no less than twenty-one bridges were destroyed in

the courses of these rivers. At the village of Bywell the flood tore the

dead bodies and coffins out of the churchyard, and bore them away,

together with many of the living inhabitants. During the same tempest an

immense number of cattle, horses, and sheep, were also transported to

the sea, while the whole coast was covered with the wreck of ships. Four

centuries before (in 1338), the same district had been visited by a

similar continuance of heavy rains, followed by disastrous floods, and

it is not improbable that these catastrophes may recur periodically,

though at uncertain intervals. As the population increases, and

buildings and bridges are multiplied, we must expect the loss of lives

and property to augment.[1080]

_Fossilization of human bodies in the bed of the sea._--If to the

hundreds of human bodies committed to the deep in the way of ordinary

burial we add those of individuals lost by shipwrecks, we shall find

that in the course of a single year, a great number of human remains are

consigned to the subaqueous regions. I shall hereafter advert to a

calculation by which it appears that more than five hundred _British_

vessels alone, averaging each a burthen of about 120 tons, are wrecked,

and sink to the bottom, _annually_. Of these the crews for the most part

escape, although it sometimes happens that all perish. In one great

naval action several thousand individuals sometimes share a watery

grave.

Many of these corpses are instantly devoured by predaceous fish,

sometimes before they reach the bottom; still more frequently when they

rise again to the surface, and float in a state of putrefaction. Many

decompose on the floor of the ocean, where no sediment is thrown down

upon them; but if they fall upon a reef where corals and shells are

becoming agglutinated into a solid rock, or subside where the delta of a

river is advancing, they may be preserved for an incalculable series of

ages.

Often at the distance of a few hundred feet from a coral reef, where

wrecks are not unfrequent, there are no soundings at the depth of many

hundred fathoms. Canoes, merchant vessels, and ships of war, may have

sunk and have been enveloped, in such situations, in calcareous sand and

breccia, detached by the breakers from the summit of a submarine

mountain. Should a volcanic eruption happen to cover such remains with

ashes and sand, and a current of lava be afterwards poured over them,

the ships and human skeletons might remain uninjured beneath the

superincumbent mass, like the houses and works of art in the

subterranean cities of Campania. Already many human remains may have

been thus preserved beneath formations more than a thousand feet in

thickness; for, in some volcanic archipelagoes, a period of thirty or

forty centuries might well be supposed sufficient for such an

accumulation. It was stated, that at the distance of about forty miles

from the base of the delta of the Ganges there is an elliptical space

about fifteen miles in diameter, where soundings of from 100 to 300

fathoms sometimes fail to reach the bottom. (See above, p. 279.) As

during the flood season the quantity of mud and sand poured by the great

rivers into the Bay of Bengal is so great that the sea only recovers its

transparency at the distance of sixty miles from the coast, this

depression must be gradually shoaling, especially as during the

monsoons, the sea loaded with mud and sand, is beaten back in that

direction towards the delta. Now, if a ship or human body sink to the

bottom in such a spot, it is by no means improbable that it may become

buried under a depth of a thousand feet of sediment in the same number

of years.

Even on that part of the floor of the ocean to which no accession of

drift matter is carried (a part which probably constitutes, at any given

period, by far the larger proportion of the whole submarine area), there

are circumstances accompanying a wreck which favor the conservation of

skeletons. For when the vessel fills suddenly with water, especially in

the night, many persons are drowned between decks and in their cabins,

so that their bodies are prevented from rising again to the surface. The

vessel often strikes upon an uneven bottom, and is overturned; in which

case the ballast, consisting of sand, shingle, and rock, or the cargo,

frequently composed of heavy and durable materials, may be thrown down

upon the carcasses. In the case of ships of war, cannon, shot, and other

warlike stores, may press down with their weight the timbers of the

vessel as they decay, and beneath these and the metallic substances the

bones of man may be preserved.

_Number of wrecked vessels._--When we reflect on the number of curious

monuments consigned to the bed of the ocean in the course of every naval

war from the earliest times, our conceptions are greatly raised

respecting the multiplicity of lasting memorials which man is leaving of

his labors. During our last great struggle with France, thirty-two of

our ships of the line went to the bottom in the space of twenty-two

years, besides seven 50-gun ships, eighty-six frigates, and a multitude

of smaller vessels. The navies of the other European powers, France,

Holland, Spain, and Denmark, were almost annihilated during the same

period, so that the aggregate of their losses must have many times

exceeded that of Great Britain. In every one of these ships were

batteries of cannon constructed of iron or brass, whereof a great number

had the dates and places of their manufacture inscribed upon them in

letters cast in metal. In each there were coins of copper, silver, and

often many of gold, capable of serving as valuable historical monuments;

in each were an infinite variety of instruments of the arts of war and

peace; many formed of materials, such as glass and earthenware, capable

of lasting for indefinite ages when once removed from the mechanical

action of the waves, and buried under a mass of matter which may exclude

the corroding action of sea-water. The quantity, moreover, of timber

which is conveyed from the land to the bed of the sea by the sinking of

ships of a large size is enormous, for it is computed that 2000 tons of

wood are required for the building of one 74-gun ship; and reckoning

fifty oaks of 100 years growth to the acre, it would require forty acres

of oak forest to build one of these vessels.[1081]

It would be an error to imagine that the fury of war is more conducive

than the peaceful spirit of commercial enterprise to the accumulation of

wrecked vessels in the bed of the sea. From an examination of Lloyd's

lists, from the year 1793 to the commencement of 1829, Captain W. H.

Smyth ascertained that the number of _British vessels_ alone lost during

that period amounted on an average to no less than one and a half

_daily_; an extent of loss which would hardly have been anticipated,

although we learn from Moreau's tables that the number of merchant

vessels employed at one time, in the navigation of England and Scotland,

amounts to about twenty thousand, having one with another a mean burthen

of 120 tons.[1082] My friend, Mr. J. L. Prevost, also informs me that on

inspecting Lloyd's list for the years 1829, 1830, and 1831, he finds

that no less than 1953 vessels were lost in those three years, their

average tonnage being about 150 tons, or in all nearly 300,000 tons,

being at the enormous rate of 100,000 tons annually of the merchant

vessels of one nation only. This increased loss arises, I presume, from

increasing activity in commerce.

Out of 551 ships of the royal navy lost to the country during the period

above mentioned, only 160 were taken or destroyed by the enemy, the rest

having either stranded or foundered, or having been burnt by accident; a

striking proof that the dangers of our naval warfare, however great, may

be far exceeded by the storm, the shoal, the lee-shore, and all the

other perils of the deep.[1083]

_Durable nature of many of their contents._--Millions of silver dollars

and other coins have been sometimes submerged in a single ship, and on

these, when they happen to be enveloped in a matrix capable of

protecting them from chemical changes, much information of historical

interest will remain inscribed, and endure for periods as indefinite as

have the delicate markings of zoophytes or lapidified plants in some of

the ancient secondary rocks. In almost every large ship, moreover, there

are some precious stones set in seals, and other articles of use and

ornament composed of the hardest substances in nature, on which letters

and various images are carved--engravings which they may retain when

included in subaqueous strata, as long as a crystal preserves its

natural form.

It was, therefore, a splendid boast, that the deeds of the English

chivalry at Agincourt made Henry's chronicle

----as rich with praise

As is the ooze and bottom of the deep

With sunken wreck and sumless treasuries

for it is probable that a greater number of monuments of the skill and

industry of man will, in the course of ages, be collected together in

the bed of the ocean, than will exist at any one time on the surface of

the continents.

If our species be of as recent a date as is generally supposed, it will

be vain to seek for the remains of man and the works of his hands

imbedded in submarine strata, except in those regions where violent

earthquakes are frequent, and the alterations of relative level so

great, that the bed of the sea may have been converted into land within

the historical era. We need not despair, however, of the discovery of

such monuments, when those regions which have been peopled by man from

the earliest ages, and which are at the same time the principal theatres

of volcanic action, shall be examined by the joint skill of the

antiquary and geologist.

_Power of human remains to resist decay._--There can be no doubt that

human remains are as capable of resisting decay as are the harder parts

of the inferior animals; and I have already cited the remark of Cuvier,

that "in ancient fields of battle the bones of men have suffered as

little decomposition as those of horses which were buried in the same

grave." (See above, p. 147.) In the delta of the Ganges bones of men

have been found in digging a well at the depth of ninety feet;[1084] but

as that river frequently shifts its course and fills up its ancient

channels, we are not called upon to suppose that these bodies are of

extremely high antiquity, or that they were buried when that part of the

surrounding delta where they occur was first gained from the sea.

_Fossil skeletons of men._--Several skeletons of men, more or less

mutilated, have been found in the West Indies, on the north-west coast

of the main land of Guadaloupe, in a kind of rock which is known to be

forming daily, and which consists of minute fragments of shells and

corals, incrusted with a calcareous cement resembling travertin, by

which also the different grains are bound together. The lens shows that

some of the fragments of coral composing this stone still retain the

same red color which is seen in the reefs of living coral which surround

the island. The shells belong to species of the neighboring sea

intermixed with some terrestrial kinds which now live on the island, and

among them is the _Bulimus Gaudaloupensis_ of Farussac. The human

skeletons still retain some of their animal matter, and all their

phosphate of lime. One of them, of which the head is wanting, may now be

seen in the British Museum, and another in the Royal Cabinet at Paris.

According to M. Konig, the rock in which the former is inclosed is

harder under the mason's saw and chisel than statuary marble. It is

described as forming a kind of glacis, probably an indurated beach,

which slants from the steep cliffs of the island to the sea, and is

nearly all submerged at high tide.

Similar formations are in progress in the whole of the West Indian

archipelago, and they have greatly extended the plain of Cayes in St.

Domingo, where fragments of vases and other human works have been found

at a depth of twenty feet. In digging wells also near Catania, in

Sicily, tools have been discovered in a rock somewhat similar.

_Buried ships, canoes, and works of art._--When a vessel is stranded in

shallow water, it usually becomes the nucleus of a sand-bank, as has

been exemplified in several of our harbors, and this circumstance tends

greatly to its preservation. Between the years 1780 and 1790 a vessel

from Purbeck, laden with three hundred tons of stone, struck on a shoal

off the entrance of Poole harbor and foundered; the crew were saved,

but the vessel and cargo remain to this day at the bottom. Since that

period the shoal at the entrance of the harbor has so extended itself in

a westerly direction towards Peveril Point in Purbeck, that the

navigable channel is thrown a mile nearer that point.[1085] The cause is

obvious; the tidal current deposits the sediment with which it is

charged around any object which checks its velocity. Matter also drifted

along the bottom is arrested by any obstacle, and accumulates round it,

just as the African sand-winds, before described, raise a small hillock

over the carcass of every dead camel exposed on the surface of the

desert.

I before alluded to an ancient Dutch vessel, discovered in the deserted

channel of the river Rother in Sussex, of which the oak wood was much

blackened, but its texture unchanged. (See above, p. 316.) The interior

was filled with fluviatile silt, as was also the case in regard to a

vessel discovered in a former bed of the Mersey, and another disinterred

where the St. Katherine Docks are excavated in the alluvial plain of the

Thames. In like manner many ships have been found preserved entire in

modern strata, formed by the silting up of estuaries along the southern

shores of the Baltic, especially in Pomerania. Between Bromberg and

Nakel, for example, a vessel and two anchors in a very perfect state

were dug up far from the sea.[1086]

Several vessels have been lately detected half buried in the delta of

the Indus, in the numerous deserted branches of that river, far from

where the stream now flows. One of these found near Vikkar in Sinde, was

400 tons in burthen, old fashioned, and pierced for fourteen guns, and

in a region where it had been matter of dispute whether the Indus had

ever been navigable by large vessels.[1087]

At the mouth of a river in Nova Scotia, a schooner of thirty-two tons,

laden with live stock, was lying with her side to the tide, when the

bore, or tidal wave, which rises there about ten feet in perpendicular

height, rushed into the estuary, and overturned the vessel, so that it

instantly disappeared. After the tide had ebbed, the schooner was so

totally buried in the sand, that the taffrel or upper rail over the

stern was alone visible.[1088] We are informed by Leigh that, on

draining Martin Meer, a lake eighteen miles in circumference, in

Lancashire, a bed of marl was laid dry, wherein no fewer than eight

canoes were found imbedded. In figure and dimensions they were not

unlike those now used in America. In a morass about nine miles distant

from this Meer a whetstone and an axe of mixed metal were dug up.[1089]

In Ayrshire, also, three canoes were found in Loch Doon some few years

ago; and during the year 1831 four others, each hewn out of separate oak

trees. They were twenty-three feet in length, two and a half in depth,

and nearly four feet in breadth at the stern. In the mud which filled

one of them was found a war-club of oak and a stone battle-axe. A canoe

of oak was also found in 1820, in peat overlying the shell-marl of the

Loch of Kinnordy, in Forfarshire.[1090]

_Manner in which ships may be preserved in a deep sea._--It is extremely

possible that the submerged woodwork of ships which have sunk where the

sea is two or three miles deep has undergone greater chemical changes in

an equal space of time, than in the cases above mentioned; for the

experiments of Scoresby show that wood may at certain depths be

impregnated in a single hour with salt water, so that its specific

gravity is entirely altered. It may often happen that hot springs,

charged with carbonate of lime, silex, and other mineral ingredients,

may issue at great depths, in which case every pore of the vegetable

tissue may be injected with the lapidifying liquid, whether calcareous

or siliceous, before the smallest decay commences. The conversion, also,

of wood into lignite is probably more rapid under enormous pressure. But

the change of the timber into lignite or coal would not prevent the

original form of a ship from being distinguished; for as we find, in

strata of the carboniferous era, the bark of the hollow reed-like trees

converted into coal, and the central cavity filled with sandstone, so

might we trace the outline of a ship in coal; while in the indurated

mud, sandstone, or limestone, filling the interior, we might discover

instruments of human art, ballast consisting of rocks foreign to the

rest of the stratum, and other contents of the ship.

_Submerged metallic substances._--Many of the metallic substances which

fall into the waters probably lose, in the course of ages, the forms

artificially imparted to them; but under certain circumstances these may

be preserved for indefinite periods. The cannon enclosed in a calcareous

rock, drawn up from the delta of the Rhone, which is now in the museum

at Montpellier, might probably have endured as long as the calcareous

matrix; but even if the metallic matter had been removed, and had

entered into new combinations, still a mould of its original shape would

have been left, corresponding to those impressions of shells which we

see in rocks, from which all the carbonate of lime has been subtracted.

About the year 1776, says Mr. King, some fishermen, sweeping for anchors

in the Gulf stream (a part of the sea near the Downs), drew up a very

curious old swivel gun, nearly eight feet in length. The barrel, which

was about five feet long, was of brass; but the handle by which it was

traversed was about three feet in length, and the swivel and pivot on

which it turned were of iron. Around these latter were formed

incrustations of sand converted into a kind of stone, of exceedingly

strong texture and firmness; whereas round the barrel of the gun, except

where it was near adjoining to the iron, there were no such

incrustations, the greater part of it being clean, and in good

condition, just as if it had still continued in use. In the incrusting

stone, adhering to it on the outside, were a number of shells and

corallines, "just as they are often found in a fossil state." These

were all so strongly attached, that it required as much force to

separate them from the matrix "as to break a fragment off any hard

rock."[1091]

In the year 1745, continues the same writer, the Fox man-of-war was

stranded on the coast of East Lothian, and went to pieces. About

thirty-three years afterwards a violent storm laid bare a part of the

wreck, and threw up near the place several masses, "consisting of iron,

ropes, and balls," covered over with ochreous sand, concreted and

hardened into a kind of stone. The substance of the rope was very little

altered. The consolidated sand retained perfect impressions of parts of

an iron ring, "just as impressions of extraneous fossil bodies are found

in various kinds of strata."[1092]

After a storm in the year 1824, which occasioned a considerable shifting

of the sands near St. Andrew's, in Scotland, a gun-barrel of ancient

construction was found, which is conjectured to have belonged to one of

the wrecked vessels of the Spanish Armada. It is now in the museum of

the Antiquarian Society of Scotland, and is incrusted over by a thin

coating of sand, the grains of which are cemented by brown ferruginous

matter. Attached to this coating are fragments of various shells, as of

the common cardium, mya, &c.

Many other examples are recorded of iron instruments taken up from the

bed of the sea near the British coast, incased by a thick coating of

conglomerate, consisting of pebbles and sand, cemented by oxide of iron.

Dr. Davy describes a bronze helmet, of the antique Grecian form, taken

up in 1825, from a shallow part of the sea, between the citadel of Corfu

and the village of Castrades. Both the interior and exterior of the

helmet were partially incrusted with shells, and a deposit of carbonate

of lime. The surface generally, both under the incrustation, and where

freed from it, was of a variegated color, mottled with spots of green,

dirty white, and red. On minute inspection with a lens, the green and

red patches proved to consist of crystals of the red oxide and carbonate

of copper, and the dirty white chiefly of oxide of tin.

The mineralizing process, says Dr. Davy, which has produced these new

combinations, has, in general, penetrated very little into the substance

of the helmet. The incrustation and rust removed, the metal is found

bright beneath; in some places considerably corroded, in others very

slightly. It proves, on analysis, to be copper, alloyed with 18.5 per

cent. of tin. Its color is that of our common brass, and it possesses a

considerable degree of flexibility.

"It is a curious question," he adds, "how the crystals were formed in

the helmet, and on the adhering calcareous deposit. There being no

reason to suppose deposition from solution, are we not under the

necessity of inferring, that the mineralizing process depends on a small

motion and separation of the particles of the original compound? This

motion may have been due to the operation of electro-chemical powers

which may have separated the different metals of the alloy.[1093]

_Effects of the Subsidence of Land, in imbedding Cities and Forests in

subaqueous Strata._

We have hitherto considered the transportation of plants and animals

from the land by _aqueous_ agents, and their inhumation in lacustrine or

submarine deposits, and we may now inquire what tendency the subsidence

of tracts of land may have to produce analogous effects. Several

examples of the sinking down of buildings, and portions of towns near

the shore, to various depths beneath the level of the sea during

subterranean movements, were before enumerated in treating of the

changes brought about by _inorganic_ causes. The events alluded to were

comprised within a brief portion of the historical period, and confined

to a small number of the regions of active volcanoes. Yet these

authentic facts, relating merely to the last century and a half, gave

indications of considerable changes in the physical geography of the

globe, and we are not to suppose that these were the only spots

throughout the surrounding land and sea which suffered similar

depressions.

If, during the short period since South America has been colonized by

Europeans, we have proof of alterations of level at the three principal

ports on the western shores, Callao, Valparaiso, and Conception,[1094]

we cannot for a moment suspect that these cities, so distant from each

other, have been selected as the peculiar points where the desolating

power of the earthquake has expended its chief fury. On considering how

small is the area occupied by the seaports of this disturbed

region--points where alone each slight change of the relative level of

the sea and land can be recognized,--and reflecting on the proofs in our

possession of the local revolutions that have happened on the site of

each port, within the last century and a half,--our conceptions must be

greatly exalted respecting the magnitude of the alterations which the

country between the Andes and the sea may have undergone, even in the

course of the last six thousand years.

_Cutch earthquake._--The manner in which a large extent of surface may

be submerged, so that the terrestrial plants and animals may be imbedded

in subaqueous strata, cannot be better illustrated than by the

earthquake of Cutch, in 1819, before alluded to (p. 460). It is stated,

that, for some years after that earthquake, the withered tamarisks and

other shrubs protruded their tops above the waves, in parts of the

lagoon formed by subsidence, on the site of the village of Sindree and

its environs; but, after the flood of 1826, they were seen no longer.

Every geologist will at once perceive, that forests sunk by such

subterranean movements may become imbedded in subaqueous deposits, both

fluviatile and marine, and the trees may still remain erect, or

sometimes the roots and part of the trunks may continue in their

original position, while the current may have broken off, or levelled

with the ground, their upper stems and branches.

_Buildings how preserved under water._--Some of the buildings which have

at different times subsided beneath the level of the sea have been

immediately covered up to a certain extent with strata of volcanic

matter showered down upon them. Such was the case at Tomboro in Sumbawa,

in the present century, and at the site of the Temple of Serapis, in the

environs of Puzzuoli, probably about the 12th century. The entrance of a

river charged with sediment in the vicinity may still more frequently

occasion the rapid envelopment of buildings in regularly stratified

formations. But if no foreign matter be introduced, the buildings, when

once removed to a depth where the action of the waves is insensible, and

where no great current happens to flow, may last for indefinite periods,

and be as durable as the floor of the ocean itself, which may often be

composed of the very same materials. There is no reason to doubt the

tradition mentioned by the classic writers, that the submerged Grecian

towns of Bura and Helice were seen under water; and it has been already

mentioned that different eye-witnesses have observed the houses of Port

Royal, at the bottom of the sea, at intervals of 88, 101, and 143 years

after the convulsion of 1692. (p. 505.)

_Buried temples of Cashmere._--The celebrated valley of Cashmere (or

Kashmir) in India, situated at the southern foot of the Himalaya range,

is about 60 miles in length, and 20 in breadth, surrounded by mountains

which rise abruptly from the plain to the height of about 5000 feet. In

the cliffs of the river Jelam and its tributaries, which traverse this

beautiful valley, strata consisting of fine clay, sand, soft sandstone,

pebbles, and conglomerate are exposed to view. They contain freshwater

shells, of the genera Lymneus, Paludina, and Cyrena, with land shells,

all of recent species, and are precisely such deposits as would be

formed if the whole valley were now converted into a great lake, and if

the numerous rivers and torrents descending from the surrounding

mountains were allowed sufficient time to fill up the lake-basin with

fine sediment and gravel. Fragments of pottery met with at the depth of

40 and 50 feet in this lacustrine formation show that the upper part of

it at least has accumulated within the human epoch.

Dr. Thomas Thomson, who visited Cashmere in 1848, observes that several

of the lakes which still exist in the great valley, such as that near

the town of Cashmere, five miles in diameter, and some others, are

deeper than the adjoining river-channels, and may have been formed by

subsidence during the numerous earthquakes which have convulsed that

region in the course of the last 2000 years. It is also probable that

the freshwater strata seen to extend far and wide over the whole of

Cashmere originated not in one continuous sheet of water once occupying

the entire valley, but in many lakes of limited area, formed and filled

in succession. Among other proofs of such lake-basins of moderate

dimensions having once existed and having been converted into land at

different periods, Dr. Thomson mentions that the ruins of Avantipura,

not far from the modern village of that name, stand on an older

freshwater deposit at the base of the mountains, and terminate abruptly

towards the plain in a straight line, such as admits of no other

explanation than by supposing that the advance of the town in that

direction was arrested by a lake, now drained or represented only by a

marsh. In that neighborhood, as very generally throughout Cashmere, the

rivers run in channels or alluvial flats, bounded by cliffs of

lacustrine strata, horizontally stratified, and these strata form low

table-lands from 20 to 50 feet high between the different watercourses.

On a table-land of this kind near Avantipura, portions of two buried

temples are seen, which have been partially explored by Major

Cunningham, who, in 1847, discovered that in one of the buildings a

magnificent colonnade of seventy-four pillars is preserved underground.

He exposed to view three of the pillars in a cavity still open. All the

architectural decorations below the level of the soil are as perfect and

fresh-looking as when first executed. The spacious quadrangle must have

been silted up gradually at first, for some unsightly alterations, not

in accordance with the general plan and style of architecture, were

detected, evidently of subsequent date, and such as could only have been

required when the water and sediment had already gained a certain height

in the interior of the temple.

This edifice is supposed to have been erected about the year 850 of our

era, and was certainly submerged before the year 1416, when the

Mahomedan king, Sikandar, called Butshikan or the idol-breaker,

destroyed all the images of Hindoo temples in Cashmere. Ferishta the

historian particularly alludes to Sikandar having demolished every

Cashmerian temple save one, dedicated to Mahadava, which escaped "in

consequence of its foundations being below the neighboring water." The

unharmed condition of the human-headed birds and other images in the

buried edifice near Avantipura leaves no doubt that they escaped the

fury of the iconoclast by being under water, and perhaps silted up

before the date of his conquest.[1095]

_Berkeley's arguments for the recent date of the creation of man._--I

cannot conclude this chapter without recalling to the reader's mind a

memorable passage written by Bishop Berkeley a century ago, in which he

inferred, on grounds which may be termed strictly geological, the recent

date of the creation of man. "To any one," says he, "who considers that

on digging into the earth, such quantities of shells, and in some

places, bones and horns of animals, are found sound and entire, after

having lain there in all probability some thousands of years; it should

seem probable that guns, medals, and implements in metal or stone, might

have lasted entire, buried under ground forty or fifty thousand years,

if the world had been so old. How comes it then to pass that no remains

are found, no antiquities of those numerous ages preceding the Scripture

accounts of time; that no fragments of buildings, no public monuments,

no intaglios, cameos, statues, basso-relievos, medals, inscriptions,

utensils, or artificial works of any kind, are ever discovered, which

may bear testimony to the existence of those mighty empires, those

successions of monarchs, heroes, and demi-gods, for so many thousand

years? Let us look forward and suppose ten or twenty thousand years to

come, during which time we will suppose that plagues, famine, wars, and

_earthquakes_ shall have made great havoc in the world, is it not highly

probable that at the end of such a period, pillars, vases, and statues

now in being, of granite, or porphyry, or jasper (stones of such

hardness as we know them to have lasted two thousand years above ground,

without any considerable alteration), would bear record of these and

past ages? Or that some of our current coins might then be dug up, or

old walls and the foundations of buildings show themselves, as well as

the shells and stones of _the primeval world_, which are preserved down

to our times."[1096]

That many signs of the agency of man would have lasted at least as long

as "the shells of the primeval world," had our race been so ancient, we

may feel as fully persuaded as Berkeley; and we may anticipate with

confidence that many edifices and implements of human workmanship and

the skeletons of men, and casts of the human form, will continue to

exist when a great part of the present mountains, continents, and seas

have disappeared. Assuming the future duration of the planet to be

indefinitely protracted, we can foresee no limit to the perpetuation of

some of the memorials of man, which are continually entombed in the

bowels of the earth or in the bed of the ocean, unless we carry forward

our views to a period sufficient to allow the various causes of change,

both igneous and aqueous, to remodel more than once the entire crust of

the earth. _One_ complete revolution will be inadequate to efface every

monument of our existence; for many works of art might enter again and

again into the formations of successive eras, and escape obliteration

even though the very rocks in which they had been for ages imbedded were

destroyed, just as pebbles included in the conglomerates of one epoch

often contain the organized remains of beings which flourished during a

prior era.

Yet it is no less true, as a late distinguished philosopher has

declared, "that none of the works of a mortal being can be

eternal."[1097] They are in the first place wrested from the hands of

man, and lost as far as regards their subserviency to his use, by the

instrumentality of those very causes which place them in situations

where they are enabled to endure for indefinite periods. And even when

they have been included in rocky strata, when they have been made to

enter as it were into the solid framework of the globe itself, they

must nevertheless eventually perish; for every year some portion of the

earth's crust is shattered by earthquakes, or melted by volcanic fire,

or ground to dust by the moving waters on the surface. "The river of

Lethe," as Bacon eloquently remarks, "runneth as well above ground as

below."[1098]

CHAPTER XLIX.

IMBEDDING OF AQUATIC SPECIES IN SUBAQUEOUS STRATA.

Inhumation of fresh water plants and animals--Shell marl--Fossilized

seed-vessels and stems of chara--Recent deposits in American

lakes--Freshwater species drifted into seas and estuaries--Lewes

levels--Alternations of marine and freshwater strata, how

caused--Imbedding of marine plants and animals--Cetacea stranded on

our shores--Littoral and estuary Testacea swept into the deep

sea--Burrowing shells--Living Testacea found at considerable

depths--Blending of organic remains of different ages.

Having treated of the imbedding of terrestrial plants and animals, and

of human remains, in deposits now forming beneath the waters, I come

next to consider in what manner _aquatic_ species may be entombed in

strata formed in their own element.

_Freshwater plants and animals._--The remains of species belonging to

those genera of the animal and vegetable kingdoms which are more or less

exclusively confined to fresh water are for the most part preserved in

the beds of lakes or estuaries, but they are oftentimes swept down by

rivers into the sea, and there intermingled with the exuviae of marine

races. The phenomena attending their inhumation in lacustrine deposits

are sometimes revealed to our observation by the drainage of small

lakes, such as are those in Scotland, which have been laid dry for the

sake of obtaining shell marl for agricultural uses.

In these recent formations, as seen in Forfarshire, two or three beds of

calcareous marl are sometimes observed separated from each other by

layers of drift peat, sand, or fissile clay. The marl often consists

almost entirely of an aggregate of shells of the genera Limnea,

Planorbis, Valvata, and Cyclas, of species now existing in Scotland. A

considerable proportion of the Testacea appear to have died very young,

and few of the shells are of a size which indicates their having

attained a state of maturity. The shells are sometimes entirely

decomposed, forming a pulverulent marl; sometimes in a state of good

preservation. They are frequently intermixed with stems of Charae and

other aquatic vegetables, the whole being matted together and

compressed, forming laminae often as thin as paper.

_Fossilized seed-vessels and stems of Chara._--As the Chara is an

aquatic plant which occurs frequently fossil in formations of different

eras, and is often of much importance to the geologist in characterizing

entire groups of strata, I shall describe the manner in which I have

found the recent species in a petrified state. They occur in a marl-lake

in Forfarshire, inclosed in nodules, and sometimes in a continuous

stratum of a kind of travertin.

[Illustration: Fig. 102.

Seed-vessel of Chara hispida.

_a_, Part of the stem with the seed-vessel attached. Magnified.

_b_, Natural size of the seed vessel.

_c_, Integument of the Gyrogonite, or petrified seed-vessel

of _Chara hispida_, found in the Scotch marl-lakes.

Magnified.

_d_, Section showing the nut within the integument.

_e_, Lower end of the integument to which the stem was attached.

_f_, Upper end of the integument to which the stigmata were attached.

_g_, One of the spiral valves of _c_.

]

The seed-vessel of these plants is remarkably tough and hard, and

consists of a membranous nut covered by an integument (_d_, fig. 102.)

both of which are spirally striated or ribbed. The integument is

composed of five spiral valves, of a quadrangular form (_g_). In _Chara

hispida_, which abounds in the lakes of Forfarshire, and which has

become fossil in the Bakie Loch, each of the spiral valves of the

seed-vessel turns rather more than twice round the circumference, the

whole together making between ten and eleven rings. The number of these

rings differs greatly in different species, but in the same appears to

be very constant.

The stems of Charae occur fossil in the Scotch marl in great abundance.

In some species, as in _Chara hispida_, the plant when living contains

so much carbonate of lime in its vegetable organization, independently

of calcareous incrustation, that it effervesces strongly with acids when

dry. The stems of _Chara hispida_ are longitudinally striated, with a

tendency to be spiral. These striae, as appears to be the case with all

Charae, turn always like the worm of a screw from right to left, while

those of the seed-vessel wind round in a contrary direction. A cross

section of the stem exhibits a curious structure, for it is composed of

a large tube surrounded by smaller tubes (fig. 103., _b_, _c_) as is

seen in some extinct as well as recent species. In the stems of several

species, however, there is only a single tube.[1099]

[Illustration: Fig. 103.

Stem and branches of Chara hispida.

_a_, Stem and branches of the natural size.

_b_, Section of the stem magnified.

_c_, Showing the central tube surrounded by two rings of smaller tubes.

]

The valves of a small animal called cypris (_C. ornata?_ Lam.) occur

completely fossilized, like the stems of Charae, in the Scotch travertin

above mentioned. The same cypris inhabits the lakes and ponds of

England, where, together with many other species, it is not uncommon.

Although extremely minute, they are visible to the naked eye, and may be

observed in great numbers, swimming swiftly through the waters of our

stagnant pools and ditches. The antennae, at the end of which are fine

pencils of hair, are the principal organs for swimming, and are moved

with great rapidity. The animal resides within two small valves, not

unlike those of a bivalve shell, and moults its integuments annually,

which the conchiferous mollusks do not. The cast-off shells, resembling

thin scales, and occurring in countless myriads in many ancient

freshwater marls, impart to them a divisional structure, like that so

frequently derived from plates of mica.

[Illustration: Fig. 104.

_Cypris unifasciata_, a living species, greatly

magnified.

_a_, Upper part. _b_, Side view of the same.

]

[Illustration: Fig. 105.]

_Cypris vidua_, a living species, greatly magnified.[1100]]

The recent strata of lacustrine origin above alluded to are of very

small extent, but analogous deposits on the grandest scale are forming

in the great Canadian lakes, as in Lakes Superior and Huron, where beds

of sand and clay are seen inclosing shells of existing species.[1101]

The Chara also plays the same part in the subaqueous vegetation of North

America as in Europe. I observed along the borders of several freshwater

lakes in the state of New York a luxuriant crop of this plant in clear

water of moderate depth, rendering the bottom as verdant as a grassy

meadow. Here, therefore, we may expect some of the tough seed vessels to

be preserved in mud, just as we detect them fossil in the Eocene strata

of Hampshire, or in the neighborhood of Paris, and many other countries.

_Imbedding of freshwater Species in Estuary and Marine Deposits._

_In Lewes levels._--We have sometimes an opportunity of examining the

deposits which within the historical period have silted up some of our

estuaries; and excavations made for wells and other purposes, where the

sea has been finally excluded, enable us to observe the state of the

organic remains in these tracts. The valley of the Ouze between Newhaven

and Lewes is one of several estuaries from which the sea has retired

within the last seven or eight centuries; and here, as appears from the

researches of Dr. Mantell, strata thirty feet and upwards in thickness

have accumulated. At the top, beneath the vegetable soil, is a bed of

peat about five feet thick, inclosing many trunks of trees. Next below

is a stratum of blue clay containing freshwater shells of about nine

species, such as now inhabit the district. Intermixed with these was

observed the skeleton of a deer. Lower down, the layers of blue clay

contain, with the above-mentioned freshwater shells, several marine

species well known on our coast. In the lowest beds, often at the depth

of thirty-six feet; these marine Testacea occur without the slightest

intermixture of fluviatile species, and amongst them the skull of the

narwal, or sea unicorn (_Monodon monoceros_), has been detected.

Underneath all these deposits is a bed of pipe-clay, derived from the

subjacent chalk.[1102]

If we had no historical information respecting the former existence of

an inlet of the sea in this valley and of its gradual obliteration, the

inspection of the section above described would show, as clearly as a

written chronicle, the following sequence of events. First, there was a

salt-water estuary peopled for many years by species of marine Testacea

identical with those now living, and into which some of the larger

Cetacea occasionally entered. Secondly, the inlet grew shallower, and

the water became brackish, or alternately salt and fresh, so that the

remains of freshwater and marine shells were mingled in the blue

argillaceous sediment of its bottom. Thirdly, the shoaling continued

until the river-water prevailed, so that it was no longer habitable by

marine Testacea, but fitted only for the abode of fluviatile species and

aquatic insects. Fourthly, a peaty swamp or morass was formed, where

some trees grew, or perhaps were drifted during floods, and where

terrestrial quadrupeds were mired. Finally, the soil being flooded by

the river only at distant intervals, became a verdant meadow.

_In delta of Ganges and Indus._--It was before stated, that on the

sea-coast, in the delta of the Ganges, there are eight great openings,

each of which has evidently, at some ancient period, served in its turn

as the principal channel of discharge.[1103] As the base of the delta is

200 miles in length, it must happen that, as often as the great volume

of river-water is thrown into the sea by a new mouth, the sea will at

one point be converted from salt to fresh, and at another from fresh to

salt; for, with the exception of those parts where the principal

discharge takes place, the salt water not only washes the base of the

delta, but enters far into every creek and lagoon. It is evident, then,

that repeated alternations of beds containing freshwater shells, with

others filled with marine exuviae, may here be formed. It has also been

shown by artesian borings at Calcutta (see above, p. 267), that the

delta once extended much farther than now into the gulf, and that the

river is only recovering from the sea the ground which had been lost by

subsidence at some former period. Analogous phenomena must sometimes be

occasioned by such alternate elevation and depression as has occurred in

modern times in the delta of the Indus.[1104] But the subterranean

movements affect but a small number of the deltas formed at one period

on the globe; whereas the silting up of some of the arms of great rivers

and the opening of others, and the consequent variation of the points

where the chief volume of their waters is discharged into the sea, are

phenomena common to almost every delta.

The variety of species of Testacea contained in the recent calcareous

marl of Scotland, before mentioned, is very small, but the abundance of

individuals extremely great, a circumstance very characteristic of

freshwater formations in general, as compared to marine; for in the

latter, as is seen on sea-beaches, coral-reefs, or in the bottom of the

seas examined by dredging, wherever the individual shells are

exceedingly numerous, there rarely fails to be a vast variety of

species.

_Imbedding of the Remains of Marine Plants and Animals._

_Marine plants._--The large banks of drift sea-weed which occur on each

side of the equator in the Atlantic, Pacific, and Indian oceans, were

before alluded to.[1105] These, when they subside, may often produce

considerable beds of vegetable matter. In Holland, submarine peat is

derived from Fuci, and on parts of our own coast from _Zostera marina_.

In places where Algae do not generate peat, they may nevertheless leave

traces of their form imprinted on argillaceous and calcareous mud, as

they are usually very tough in their texture.

Sea-weeds are often cast up in such abundance on our shores during heavy

gales, that we cannot doubt that occasionally vast numbers of them are

imbedded in littoral deposits now in progress. We learn from the

researches of Dr. Forchhammer, that besides supplying in common with

land plants the materials of coal, the Algae must give rise to important

chemical changes in the composition of strata in which they are

imbedded. These plants always contain sulphuric acid, and sometimes in

as large a quantity as 8-1/2 per cent., combined with potash: magnesia

also and phosphoric acid are constant ingredients. Whenever large masses

of sea-weeds putrefy in contact with ferruginous clay, sulphuret of

iron, or iron pyrites, is formed by the union of the sulphur of the

plants with the iron of the clay; while the potash, released from its

union with the clay (_i. e._ silicate of alumina), forms with it a

peculiar compound. Many of the mineral characteristics of ancient rocks,

especially the alum slates, and the pyrites which occur in clay slate,

and the fragments of anthracite in marine Silurian strata, may be

explained by the decomposition of fucoids or sea-weeds.[1106]

_Imbedding of cetacea._--It is not uncommon for the larger Cetacea,

which can float only in a considerable depth of water, to be carried

during storms or high tides into estuaries, or upon low shores, where,

upon the retiring of high water, they are stranded. Thus a narwal

(_Monodon monoceros_) was found on the beach, near Boston in

Lincolnshire, in the year 1800, the whole of its body buried in the mud.

A fisherman going to his boat saw the horn, and tried to pull it out,

when the animal began to stir itself.[1107] An individual of the common

whale (_Balaena mysticetus_), which measured seventy feet,

came ashore near Peterhead, in 1682. Many individuals of the genus

Balaenoptera have met the same fate. It will be sufficient to refer to

those cast on shore near Burnt Island, and at Alloa, recorded by Sibbald

and Neill. The other individual mentioned by Sibbald, as having come

ashore at Boyne, in Banffshire, was probably a razor-back. Of the genus

Catodon (_Cachalot_), Ray mentions a large one stranded on the west

coast of Holland in 1598, and the fact is also commemorated in a Dutch

engraving of the time of much merit. Sibbald, too, records that a herd

of Cachalots, upwards of 100 in number, were found stranded at

Cairston, in Orkney. The dead bodies of the larger Cetacea are sometimes

found floating on the surface of the waters, as was the case with the

immense whale exhibited in London in 1831. And the carcase of a sea-cow

or Lamantine (_Halicora_) was, in 1785, cast ashore near Leith.

To some accident of this kind we may refer the position of the skeleton

of a whale, seventy-three feet long, which was found at Airthrey, on the

Forth, near Stirling, imbedded in clay twenty feet higher than the

surface of the highest tide of the river Forth at the present day. From

the situation of the Roman station and causeways at a small distance

from the spot, it is concluded that the whale must have been stranded

there at a period prior to the Christian era.[1108]

Other fossil remains of this class have also been found in estuaries

known to have been silted up in recent times, one example of which has

been already mentioned near Lewes, in Sussex.

[Illustration: Fig. 106.

Fossil eggs of turtles from the Island of Ascension.[1109]]

_Marine reptiles._--Some singular fossils have lately been discovered in

the Island of Ascension, in a stone said to be continually forming on

the beach, where the waves threw up small rounded fragments of shells

and corals, which, in the course of time, become firmly agglutinated

together, and constitute a stone used largely for building and making

lime. In a quarry on the N. W. side of the island, about 100 yards from

the sea, some fossil eggs of turtles have been discovered in the hard

rock thus formed. The eggs must have been nearly hatched at the time

when they perished; for the bones of the young turtle are seen in the

interior, with their shape fully developed, the interstices between the

bones being entirely filled with grains of sand, which are cemented

together, so that when the egg-shells are removed perfect casts of their

form remain in stone. In the single specimen here figured (fig. 106),

which is only five inches in its longest diameter, no less than seven

eggs are preserved.[1110]

To explain the state in which they occur fossil, it seems necessary to

suppose that after the eggs were almost hatched in the warm sand, a

great wave threw upon them so much more sand as to prevent the rays of

the sun from penetrating, so that the yolk was chilled and deprived of

vitality. The shells were, perhaps, slightly broken at the same time,

so that small grains of sand might gradually be introduced into the

interior by water as it percolated through the beach.

[Illustration: Fig. 107.

One of the eggs in fig. 106, of the natural size, showing the bones of

the foetus which had been nearly hatched.]

_Marine testacea._--The aquatic animals and plants which inhabit an

estuary are liable, like the trees and land animals which people the

alluvial plains of a great river, to be swept from time to time far into

the deep; for as a river is perpetually shifting its course, and

undermining a portion of its banks with the forests which cover them, so

the marine current alters its direction from time to time, and bears

away the banks of sand and mud against which it turns its force. These

banks may consist in great measure of shells peculiar to shallow and

sometimes brackish water, which may have been accumulating for

centuries, until at length they are carried away and spread out along

the bottom of the sea, at a depth at which they could not have lived and

multiplied. Thus littoral and estuary shells are more frequently liable

even than freshwater species, to be intermixed with the exuviae of

pelagic tribes.

After the storm of February 4, 1831, when several vessels were wrecked

in the estuary of the Forth, the current was directed against a bed of

oysters with such force, that great heaps of them were thrown _alive_

upon the beach, and remained above high-water mark. I collected many of

these oysters, as also the common eatable whelks (_Buccina_), thrown up

with them, and observed that, although still living, their shells were

worn by the long attrition of sand which had passed over them as they

lay in their native bed, and which had evidently not resulted from the

mere action of the tempest by which they were cast ashore.

From these facts we learn that the union of the two parts of a bivalve

shell does not prove that it has not been transported to a distance;

and when we find shells worn, and with all their prominent parts rubbed

off, they may still have been imbedded where they grew.

_Burrowing shells._--It sometimes appears extraordinary, when we observe

the violence of the breakers on our coast, and see the strength of the

current in removing cliffs, and sweeping out new channels, that many

tender and fragile shells should inhabit the sea in the immediate

vicinity of this turmoil. But a great number of the bivalve Testacea,

and many also of the turbinated univalves, burrow in sand or mud. The

Solen and the Cardium, for example, which are usually found in shallow

water near the shore, pierce through a soft bottom without injury to

their shells; and the Pholas can drill a cavity through mud of

considerable hardness. The species of these and many other tribes can

sink, when alarmed, with considerable rapidity, often to the depth of

several feet, and can also penetrate upwards again to the surface, if a

mass of matter be heaped upon them. The hurricane, therefore, may expend

its fury in vain, and may sweep away even the upper part of banks of

sand or mud, or may roll pebbles over them, and yet these Testacea may

remain below secure and uninjured.

_Shells become fossil at considerable depths._--I have already stated

that, at the depth of 950 fathoms, between Gibraltar and Ceuta, Captain

Smith found a gravelly bottom, with fragments of broken shells, carried

thither probably from the comparatively shallow parts of the neighboring

straits, through which a powerful current flows. Beds of shelly sand

might here, in the course of ages, be accumulated several thousand feet

thick. But, without the aid of the drifting power of a current, shells

may accumulate in the spot where they live and die, at great depths from

the surface, if sediment be thrown down upon them; for even in our own

colder latitudes, the depths at which living marine animals abound is

very considerable. Captain Vidal ascertained, by soundings made off Tory

Island, on the northwest coast of Ireland, that Crustacea, Star-fish,

and Testacea occurred at various depths between fifty and one hundred

fathoms; and he drew up Dentalia from the mud of Galway Bay, in 230 and

240 _fathoms_ water.

The same hydrographer discovered on the Rockhall Bank large quantities

of shells at depths varying from 45 to 190 fathoms. The shells were for

the most part pulverized, and evidently recent, as they retained their

colors. In the same region a bed of fish bones was observed extending

for two miles along the bottom of the sea in eighty and ninety fathoms

water. At the eastern extremity also of Rockhall Bank, fishbones were

met with, mingled with pieces of fresh shell, at the depth of 235

fathoms.

Analogous formations are in progress in the submarine tracts extending

from the Shetland Isles to the north of Ireland, wherever soundings can

be procured. A continuous deposit of sand and mud, replete with broken

and entire shells, Echini, &c., has been traced for upwards of twenty

miles to the eastward of the Faroe Islands, usually at the depth of from

forty to one hundred fathoms. In one part of this tract (lat. 61 degrees

50 minutes, long. 6 degrees 30 minutes) fish-bones occur in

extraordinary profusion, so that the lead cannot be drawn up without

some vertebrae being attached. This "bone bed," as it was called by our

surveyors, is three miles and a half in length, and forty-five fathoms

under water, and contains a few shells intermingled with the bones.

In the British seas, the shells and other organic remains lie in soft

mud or loose sand and gravel; whereas, in the bed of the Adriatic,

Donati found them frequently inclosed in stone of recent origin. This is

precisely the difference in character which we might have expected to

exist between the British marine formations now in progress and those of

the Adriatic; for calcareous and other mineral springs abound in the

Mediterranean and lands adjoining, while they are almost entirely

wanting in our own country. I have already adverted to the eight regions

of different depths in the AEgean Sea, each characterized by a peculiar

assemblage of shells, which have been described by Professor E. Forbes,

who explored them by dredging. (See above, p. 649.)

During his survey of the west coast of Africa, Captain Sir E. Belcher

found, by frequent soundings between the twenty-third and twentieth

degrees of north latitude, that the bottom of the sea, at the depth of

from twenty to about fifty fathoms, consists of sand with a great

intermixture of shells, often entire, but sometimes finely comminuted.

Between the eleventh and ninth degrees of north latitude, on the same

coast, at soundings varying from twenty to about eighty fathoms, he

brought up abundance of corals and shells mixed with sand. These also

were in some parts entire, and in others worn and broken.

In all these cases, it is only necessary that there should be some

deposition of sedimentary matter, however minute, such as may be

supplied by rivers draining a continent, or currents preying on a line

of cliffs, in order that stratified formations, hundreds of feet in

thickness, and replete with organic remains, should result in the course

of ages.

But although some deposits may thus extend continuously for a thousand

miles or more near certain coasts, the greater part of the bed of the

ocean, remote from continents and islands, may very probably receive, at

the same time, no new accessions of drift matter, all sediment being

intercepted by intervening hollows, in which a marine current must clear

its waters as thoroughly as a turbid river in a lake. Erroneous theories

in geology may be formed not only from overlooking the great extent of

simultaneous deposits now in progress, but also from the assumption that

such formations may be universal or coextensive with the bed of the

ocean.

We frequently observe, on the sea beach, very perfect specimens of

fossil shells, quite detached from their matrix, which have been washed

out of older formations, constituting the sea-cliffs. They may be all of

extinct species, like the Eocene freshwater and marine shells strewed

over the shores of Hampshire, yet when they become mingled with the

shells of the present period, and buried in the same deposits of mud and

sand, they would appear, if upraised and examined by future geologists,

to have been all of the same age. That such intermixture and blending

of organic remains of different ages have actually taken place in former

times, is unquestionable, though the occurrence appears to be very local

and exceptional. It is, however, a class of accidents more likely than

almost any other to lead to serious anachronisms in geological

chronology.

CHAPTER L.

FORMATION OF CORAL REEFS.

Growth of coral chiefly confined to tropical regions--Principal

genera of coral-building zoophytes--Their rate of growth--Seldom

flourish at greater depths than twenty fathoms--Atolls or annular

reefs with lagoons--Maldive Isles--Origin of the circular

form--Coral reefs not based on submerged volcanic craters--Mr.

Darwin's theory of subsidence in explanation of atolls, encircling

and barrier reefs--Why the windward side of atolls

highest--Subsidence explains why all atolls are nearly on one

level--Alternate areas of elevation and subsidence--Origin of

openings into the lagoons--Size of atolls and barrier

reefs--Objection to the theory of subsidence

considered--Composition, structure, and stratified arrangement of

rocks now forming in coral reefs--Lime, whence derived--Supposed

increase of calcareous matter in modern epochs

controverted--Concluding remarks.

The powers of the organic creation in modifying the form and structure

of the earth's crust, are most conspicuously displayed in the labors of

the coral animals. We may compare the operation of these zoophytes in

the ocean, to the effects produced on a smaller scale upon the land by

the plants which generate peat. In the case of the Sphagnum, the upper

part vegetates while the lower part is entering into a mineral mass, in

which the traces of organization remain when life has entirely ceased.

In corals, in like manner, the more durable materials of the generation

that has passed away serve as the foundation on which the living animals

continue to rear a similar structure.

The stony part of the lamelliform zoophyte may be likened to an internal

skeleton; for it is always more or less surrounded by a soft animal

substance capable of expanding itself; yet, when alarmed, it has the

power of contracting and drawing itself almost entirely into the cells

and hollows of the hard coral. Although oftentimes beautifully colored

in their own element, the soft parts become when taken from the sea

nothing more in appearance than a brown slime spread over the stony

nucleus.[1111]

The growth of those corals which form reefs of solid stone is entirely

confined to the warmer regions of the globe, rarely extending beyond the

tropics above two or three degrees, except under peculiar circumstances,

as in the Bermuda Islands, in lat. 32 degrees N., where the Atlantic is

warmed by the Gulf stream. The Pacific Ocean, throughout a space

comprehended between the thirtieth parallels of latitude on each side of

the equator, is extremely productive of coral; as also are the Arabian

and Persian Gulfs. Coral is also abundant in the sea between the coast

of Malabar and the island of Madagascar. Flinders describes a reef of

coral on the east coast of New Holland as having a length of nearly 1000

miles, and as being in one part unbroken for a distance of 350 miles.

Some groups of coral islands in the Pacific are from 1100 to 1200 miles

in length, by 300 or 400 in breadth, as the Dangerous Archipelago, for

example, and that called Radack by Kotzebue; but the islands within

these spaces are always small points, and often very thinly sown.

[Illustration: Fig. 108.

_Meandrina labyrinthica_, Lam.]

Of the numerous species of zoophytes which are engaged in the production

of coral banks, some of the most common belong to the Lamarckian genera

Astrea, Porites, Madrepora, Millepora, Caryophyllia, and Meandrina.

_Rate of the growth of Coral._--Very different opinions have been

entertained in regard to the rate at which coral reefs increase. In

Captain Beechey's late expedition to the Pacific, no positive

information could be obtained of any channel having been filled up

within a given period; and it seems established, that several reefs had

remained for more than half a century, at about the same depth from the

surface.

Ehrenberg also questions the fact of channels and harbors having been

closed up in the Red Sea by the rapid increase of coral limestone. He

supposes the notion to have arisen from the circumstance of havens

having been occasionally filled up in some places with coral sand, in

others with large quantities of ballast of coral rock thrown down from

vessels.

[Illustration: Genera of Zoophytes most common in coral reefs.

Fig. 109.

_Astrea dipsacea_, Lam.]

[Illustration: Fig. 110.

Extremity of branch of _Madrepora muricata_, Lin.]

[Illustration: Fig. 111.

_Caryophyllia fastigiata_, Lam.]

[Illustration: Fig. 112.

_Porites clavaria_, Lam.]

[Illustration: Fig. 113.

_Oculina hirtella_, Lam.]

The natives of the Bermuda Islands point out certain corals now growing

in the sea, which, according to tradition, have been living in the same

spots for centuries. It is supposed that some of them may vie in age

with the most ancient trees of Europe. Ehrenberg also observed single

corals of the genera Meandrina and Favia, having a globular form, from

six to nine feet in diameter, "which must (he says) be of immense

antiquity, probably several thousand years old, so that Pharaoh may have

looked upon these same individuals in the Red Sea."[1112] They certainly

imply, as he remarks, that the reef on which they grow has increased at

a very slow rate. After collecting more than 100 species, he found none

of them covered with parasitic zoophytes, nor any instance of a living

coral growing on another living coral. To this repulsive power which

they exert whilst living, against all others of their own class, we owe

the beautiful symmetry of some large Meandrinae, and other species which

adorn our museums. Yet Balani and Serpulae can attach themselves to

living corals, and holes are excavated in them by saxicavous mollusca.

At the island called Taaopoto, in the South Pacific, the anchor of a

ship, wrecked about 50 years before, was observed in seven fathoms

water, still preserving its original form, but entirely incrusted by

coral.[1113] This fact would seem to imply a slow rate of augmentation;

but to form a correct estimate of the average rate must be very

difficult, since it must vary not only according to the species of

coral, but according to the circumstances under which each species may

be placed; such, for example, as the depth from the surface, the

quantity of light, the temperature of the water, its freedom from sand

or mud, or the absence or presence of breakers, which is favorable to

the growth of some kinds and is fatal to that of others. It should also

be observed that the apparent stationary condition of some coral reefs,

which according to Beechey have remained for centuries at the same depth

under water, may be due to subsidence, the upward growth of the coral

having been just sufficient to keep pace with the sinking of the solid

foundation on which the zoophytes have built. We shall afterwards see

how far this hypothesis is borne out by other evidence in the regions of

annular reefs or atolls.

In one of the Maldive islands a coral reef, which, within a few years,

existed on an islet bearing cocoa-nut trees, was found by Lieutenant

Prentice, "_entirely covered with live coral and madrepore_." The

natives stated that the islet had been washed away by a change in the

currents, and it is clear that a coating of growing coral had been

formed in a short time.[1114] Experiments, also, of Dr. Allan, on the

east coast of Madagascar, prove the possibility of coral growing to a

thickness of three feet in about half a year,[1115] so that the rate of

increase may, under favorable circumstances, be very far from slow.

It must not be supposed that the calcareous masses termed coral reefs

are exclusively the work of zoophytes: a great variety of shells, and,

among them, some of the largest and heaviest of known species,

contribute to augment the mass. In the South Pacific, great beds of

oysters, mussels, _Pinnae marinae_, _Chamoe_ (or _Tridacnae_), and other

shells, cover in profusion almost every reef; and on the beach of coral

islands are seen the shells of echini and broken fragments of

crustaceous animals. Large shoals of fish are also discernible through

the clear blue water, and their teeth and hard palates cannot fail to be

often preserved although their soft cartilaginous bones may decay.

It was the opinion of the German naturalist Forster, in 1780, after his

voyage round the world with Captain Cook, that coral animals had the

power of building up steep and almost perpendicular walls from great

depths in the sea, a notion afterwards adopted by Captain Flinders and

others; but it is now very generally believed that these zoophytes

cannot live in water of great depths.

Mr. Darwin has come to the conclusion, that those species which are most

effective in the construction of reefs, rarely flourish at a greater

depth than 20 fathoms, or 120 feet. In some lagoons, however, where the

water is but little agitated, there are, according to Kotzebue, beds of

living coral in 25 fathoms of water, or 150 feet; but these may perhaps

have begun to live in shallower water, and may have been carried

downwards by the subsidence of the reef. There are also various species

of zoophytes, and among them some which are provided with calcareous as

well as horny stems, which live in much deeper water, even in some cases

to a depth of 180 fathoms; but these do not appear to give origin to

stony reefs.

There is every variety of form in coral reefs, but the most remarkable

and numerous in the Pacific consist of circular or oval strips of dry

land, enclosing a shallow lake or lagoon of still water, in which

zoophytes and mollusca abound. These annular reefs just raise themselves

above the level of the sea, and are surrounded by a deep and often

unfathomable ocean.

In the annexed cut (fig. 114), one of these circular islands is

represented, just rising above the waves, covered with the cocoa-nut and

other trees, and inclosing within a lagoon of tranquil water.

[Illustration: Fig. 114.

View of Whitsunday Island. (Capt. Beechey.)[1116]]

The accompanying section will enable the reader to comprehend the usual

form of such islands. (Fig. 115.)

[Illustration: Fig. 115.

Section of a Coral Island.

_a_, _a_, Habitable part of the island, consisting of a strip

of coral, inclosing the lagoon.

_b_, _b_, The lagoon.

]

The subjoined cut (fig. 116.) exhibits a small part of the section of a

coral island on a larger scale.

[Illustration: Fig. 116.

Section of part of a Coral Island.

_a_, _b_, Habitable part of the island.

_b_, _c_, Slope of the side of the island, plunging at an angle of

forty-five to the depth of fifteen hundred feet.

_c_, _c_, Part of the lagoon.

_d_, _d_, Knolls of coral in the lagoon, with overhanging masses of

coral resembling the capitals of columns.]

Of thirty-two of these coral islands visited by Beechey in his voyage to

the Pacific, twenty-nine had lagoons in their centres. The largest was

30 miles in diameter, and the smallest less than a mile. All were

increasing their dimensions by the active operations of the lithophytes,

which appeared to be gradually extending and bringing the immersed parts

of their structure to the surface. The scene presented by these annular

reefs is equally striking for its singularity and beauty. A strip of

land a few hundred yards wide is covered by lofty cocoa-nut trees, above

which is the blue vault of heaven. This band of verdure is bounded by a

beach of glittering white sand, the outer margin of which is encircled

with a ring of snow-white breakers, beyond which are the dark heaving

waters of the ocean. The inner beach incloses the still clear water of

the lagoon, resting in its greater part on white sand, and when

illuminated by a vertical sun, of a most vivid green.[1117] Certain

species of zoophytes abound most in the lagoon, others on the exterior

margin, where there is a great surf. "The ocean," says Mr. Darwin,

"throwing its breakers on these outer shores, appears an invincible

enemy, yet we see it resisted and even conquered by means which at first

seem most weak and inefficient. No periods of repose are granted, and

the long swell caused by the steady action of the trade wind never

ceases. The breakers exceed in violence those of our temperate regions,

and it is impossible to behold them without feeling a conviction that

rocks of granite or quartz would ultimately yield and be demolished by

such irresistible forces. Yet these low insignificant coral islets stand

and are victorious, for here another power, as antagonist to the former,

takes part in the contest. The organic forces separate the atoms of

carbonate of lime one by one from the foaming breakers, and unite them

into a symmetrical structure; myriads of architects are at work night

and day, month after month, and we see their soft and gelatinous bodies

through the agency of the vital laws conquering the great mechanical

power of the waves of an ocean, which neither the art of man, nor the

inanimate works of nature could successfully resist."[1118]

As the coral animals require to be continually immersed in salt water,

they cannot raise themselves by their own efforts, above the level of

the lowest tides. The manner in which the reefs are converted into

islands above the level of the sea is thus described by Chamisso, a

naturalist, who accompanied Kotzebue in his voyages:--"When the reef,"

says he, "is of such a height that it remains almost dry at low water

the corals leave off building. Above this line a continuous mass of

solid stone is seen composed of the shells of mollusks and echini, with

their broken-off prickles and fragments of coral, united by calcareous

sand, produced by the pulverization of shells. The heat of the sun often

penetrates the mass of stone when it is dry, so that it splits in many

places, and the force of the waves is thereby enabled to separate and

lift blocks of coral, frequently six feet long and three or four in

thickness, and throw them upon the reef, by which means the ridge

becomes at length so high that it is covered only during some seasons of

the year by the spring tides. After this the calcareous sand lies

undisturbed, and offers to the seeds of trees and plants cast upon it by

the waves a soil upon which they rapidly grow, to overshadow its

dazzling white surface. Entire trunks of trees, which are carried by the

rivers from other countries and islands, find here, at length, a

resting-place after their long wanderings: with these come some small

animals such as insects and lizards, as the first inhabitants. Even

before the trees form a wood, the sea-birds nestle here; stray

land-birds take refuge in the bushes; and, at a much later period, when

the work has been long since completed, man appears and builds his hut

on the fruitful soil."[1119]

In the above description the solid stone is stated to consist of shell

and coral, united by sand; but masses of very compact limestone are also

found even in the uppermost and newest parts of the reef, such as could

only have been produced by chemical precipitation. Professor Agassiz

also informs me that his observations on the Florida reefs (which

confirm Darwin's theory of atolls to be mentioned in the sequel) have

convinced him, that large blocks are loosened, not by shrinkage in the

sun's heat, as Chamisso imagined, but by innumerable perforations of

lithodomi and other boring testacea.

The carbonate of lime may have been principally derived from the

decomposition of corals and testacea; for when the animal matter

undergoes putrefaction, the calcareous residuum must be set free under

circumstances very favorable to precipitation, especially when there are

other calcareous substances, such as shells and corals, on which it may

be deposited. Thus organic bodies may be inclosed in a solid cement, and

become portions of rocky masses.[1120]

The width of the circular strip of dead coral forming the islands

explored by Captain Beechey, exceeded in no instance half a mile from

the usual wash of the sea to the edge of the lagoon, and, in general,

was only about three or four hundred yards.[1121] The depth of the

lagoons is various; in some, entered by Captain Beechey, it was from

twenty to thirty-eight fathoms.

The two other peculiarities which are most characteristic of the annular

reef or atoll are first, that the strip of dead coral is invariably

highest on the windward side, and secondly, that there is very generally

an opening at some point in the reef affording a narrow passage, often

of considerable depth, from the sea into the lagoon.

[Illustration: Fig. 117.]

_Maldive and Laccadive Isles._--The chain of reefs and islets called the

Maldives (see fig. 117.), situated in the Indian Ocean, to the

south-west of Malabar, forms a chain 470 geographical miles in length,

running due north and south, with an average breadth of about 50 miles.

It is composed throughout of a series of circular assemblages of islets,

all formed of coral, the larger groups being from forty to ninety miles

in their longest diameter. Captain Horsburgh, whose chart of these

islands is subjoined, states, that outside of each circle or _atoll_, as

it is termed, there are coral reefs sometimes extending to the distance

of two or three miles, beyond which there are no soundings at immense

depths. But in the centre of each atoll there is a lagoon from fifteen

to forty-nine fathoms deep. In the channels between the atolls no

soundings can usually be obtained at the depth of 150 or even 250

fathoms, but during Captain Moresby's survey, soundings were struck at

150 and 200 fathoms, the only instances as yet known of the bottom

having been reached, either in the Indian or Pacific oceans, in a space

intervening between two separate and well characterized atolls.

The singularity in the form of the atolls of this archipelago consists

in their being made up, not of one continuous circular reef but of a

ring of small coral islets sometimes more than a hundred in number, each

of which is a miniature atoll in itself; in other words, a ring-shaped

strip of coral surrounding a lagoon of salt water. To account for the

origin of these, Mr. Darwin supposes the larger annular reef to have

been broken up into a number of fragments, each of which acquired its

peculiar configurations under the influence of causes similar to those

to which the structure of the parent atoll has been due. Many of the

minor rings are no less than three, and even five miles in diameter, and

some are situated in the midst of the principal lagoon; but this happens

only in cases where the sea can enter freely through breaches in the

outer or marginal reef.

The rocks of the Maldives are composed of sandstone formed of broken

shells and corals, such as may be obtained in a loose state from the

beach, and which is seen when exposed for a few days to the air to

become hardened. The sandstone is sometimes observed to be an aggregate

of broken shells, corals, pieces of wood, and shells of the

cocoa-nut.[1122]

The Laccadive islands run in the same line with the Maldives, on the

north, as do the isles of the Chagos Archipelago, on the south; so that

these may be continuations of the same chain of submerged mountains,

crested in a similar manner by coral limestones.

_Origin of the circular form--not volcanic._--The circular and oval

shape of so many reefs, each having a lagoon in the centre, and being

surrounded on all sides by a deep ocean, naturally suggested the idea

that they were nothing more than the crests of submarine volcanic

craters overgrown by coral; and this theory I myself advocated in the

earlier editions of this work. Although I am now about to show that it

must be abandoned, it may still be instructive to point out the grounds

on which it was formerly embraced. In the first place, it had been

remarked that there were many active volcanoes in the coral region of

the Pacific, and that in some places, as in Gambier's group, rocks

composed of porous lava rise up in a lagoon bordered by a circular reef,

just as the two cones of eruption called the Kamenis have made their

appearance in the times of history within the circular gulf of

Santorin.[1123] It was also observed that, as in S. Shetland, Barren

Island, and others of volcanic origin, there is one narrow breach in the

walls of the outer cone by which ships may enter a circular gulf, so in

like manner there is often a single deep passage leading into the lagoon

of a coral island, the lagoon itself seeming to represent the hollow or

gulf just as the ring of dry coral recalls to our minds the rim of a

volcanic crater. More lately, indeed, Mr. Darwin has shown that the

numerous volcanic craters of the Galapagos Archipelago in the Pacific

have all of them their southern sides the lowest, or in many cases quite

broken down, so that if they were submerged and incrusted with coral,

they would resemble true atolls in shape.[1124]

Another argument which I adduced when formerly defending this doctrine

was derived from Ehrenberg's statement, that some banks of coral in the

Red Sea were square, while many others were ribbon-like strips, with

flat tops, and without lagoons. Since, therefore, all the genera and

many of the species of zoophytes in the Red Sea agreed with those which

elsewhere construct lagoon islands, it followed that the stone-making

zoophytes are not guided by their own instinct in the formation of

annular reefs, but that this peculiar shape and the position of such

reefs in the midst of a deep ocean must depend on the outline of the

submarine bottom, which resembles nothing else in nature but the crater

of a lofty submerged volcanic cone. The enormous size, it is true, of

some atolls, made it necessary for me to ascribe to the craters of many

submarine volcanoes a magnitude which was startling, and which had often

been appealed to as a serious objection to the volcanic theory. That so

many of them were of the same height, or just level with the water, did

not present a difficulty so long as we remained ignorant of the fact

that the reef-building species do not grow at greater depths than

twenty-five fathoms.

_May be explained by subsidence._--Mr. Darwin, after examining a variety

of coral formations in different parts of the globe, was induced to

reject the opinion that their shape represented the form of the original

bottom. Instead of admitting that the ring of dead coral rested on a

circular or oval ridge of rock, or that the lagoon corresponded to a

preexisting cavity, he advanced a new opinion, which must, at first

sight, seem paradoxical in the extreme; namely, that the lagoon is

precisely in the place once occupied by the highest part of a

mountainous island, or, in other cases, by the top of a shoal.

The following is a brief sketch of the facts and arguments in favor of

this new view:--Besides those rings of dry coral which enclose lagoons,

there are others having a similar form and structure which encircle

lofty islands. Of the latter kind is Vanikoro, (see map, fig. 39, p.

351,) celebrated on account of the shipwreck of La Peyrouse, where the

coral reef runs at the distance of two or three miles from the shore,

the channel between it and the land having a general depth of between

200 and 300 feet. This channel, therefore, is analogous to a lagoon, but

with an island standing in the middle like a picture in its frame. In

like manner in Tahiti we see a mountainous land, with everywhere round

its margin a lake or zone of smooth salt water, separated from the ocean

by an encircling reef of coral, on which a line of breakers is always

foaming. So also New Caledonia, a long narrow island east of New

Holland, in which the rocks are granitic, is surrounded by a reef which

runs for a length of 400 miles. This reef encompasses not only the

island itself, but a ridge of rocks which are prolonged in the same

direction beneath the sea. No one, therefore, will contend for a moment

that in this case the corals are based upon the rim of a volcanic

crater, in the middle of which stands a mountain or island of granite.

The great barrier reef, already mentioned as running parallel to the

north-east coast of Australia for nearly 1000 miles, is another most

remarkable example of a long strip of coral running parallel to a coast.

Its distance from the mainland varies from twenty to seventy miles, and

the depth of the great arm of the sea thus enclosed is usually between

ten and twenty fathoms, but towards one end from forty to sixty. This

great reef would extend much farther, according to Mr. Jukes, if the

growth of coral were not prevented off the shores of New Guinea by a

muddy bottom, caused by rivers charged with sediment which flow from the

southern coast of that great island.[1125]

Two classes of reefs, therefore, have now been considered; first, the

atoll, and, secondly, the encircling and barrier reef, all agreeing

perfectly in structure, and the sole difference lying in the absence in

the case of the atoll of all land, and in the others the presence of

land bounded either by an encircling or a barrier reef. But there is

still a third class of reefs, called by Mr. Darwin "fringing reefs,"

which approach much nearer the land than those of the encircling and

barrier class, and which indeed so nearly touched the coast as to leave

nothing in the intervening space resembling a lagoon. "That these reefs

are not attached quite close to the shore appears to be the result of

two causes; first, that the water immediately adjoining the beach is

rendered turbid by the surf, and therefore injurious to all zoophytes;

and, secondly, that the larger and efficient kinds only flourish on the

outer edge amidst the breakers of the open sea."[1126]

[Illustration: Fig. 118.

Supposed section of an island with an encircling reef of coral.

A, The island.

_b_, _c_, Highest points of the encircling reef between which and the

coast is seen a space occupied by still water.]

It will at once be conceded that there is so much analogy between the

form and position of the strip of coral in the atoll, and in the

encircling and barrier reef, that no explanation can be satisfactory

which does not include the whole. If we turn in the first place to the

encircling and barrier reefs, and endeavor to explain how the zoophytes

could have found a bottom on which to begin to build, we are met at once

with a great difficulty. It is a general fact, long since remarked by

Dampier, that high land and deep seas go together. In other words, steep

mountains coming down abruptly to the sea-shore are generally continued

with the same slope beneath the water. But where the reef, as at _b_ and

_c_ (fig. 118), is distant several miles from a steep coast, a line

drawn perpendicularly downwards from its outer edges _b c_ to the

fundamental rock _d e_, must descend to a depth exceeding by several

thousand feet the limits at which the efficient stone-building corals

can exist, for we have seen that they cease to grow in water which is

more than 120 feet deep. That the original root immediately beneath the

points _b c_ is actually as far from the surface as _d e_, is not merely

inferred from Dampier's rule, but confirmed by the fact, that,

immediately outside the reef, soundings are either not met with at all,

or only at enormous depths. In short, the ocean is as deep there as

might have been anticipated in the neighborhood of a bold coast; and it

is obviously the presence of the coral alone which has given rise to the

anomalous existence of shallow water on the reef and between it and the

land.

After studying in minute detail all the phenomena above described, Mr.

Darwin has offered in explanation a theory now very generally adopted.

The coral-forming polypi, he states, begin to build in water of a

moderate depth, and while they are yet at work, the bottom of the sea

subsides gradually, so that the foundation of their edifice is carried

downwards at the same time that they are raising the superstructure. If,

therefore, the rate of subsidence be not too rapid, the growing coral

will continue to build up to the surface; the mass always gaining in

height above its original base, but remaining in other respects in the

same position. Not so with the land; each inch lost is irreclaimably

gone; as it sinks, the water gains foot by foot on the shore, till in

many cases the highest peak of the original island disappears. What was

before land is then occupied by the lagoon, the position of the

encircling coral remaining unaltered, with the exception of a slight

contraction of its dimensions.

In this manner are encircling reefs and atolls produced; and in

confirmation of his views Mr. Darwin has pointed out examples which

illustrate every intermediate state, from that of lofty islands, such as

Otaheite, encircled by coral, to that of Gambier's group, where a few

peaks only of land rise out of a lagoon, and lastly, to the perfect

atoll, having a lagoon several hundred feet deep, surrounded by a reef

rising steeply from an unfathomed ocean.

[Illustration: Fig. 119.]

If we embrace these views, it is clear, that in regions of growing coral

a similar subsidence must give rise to barrier reefs along the shores of

a continent. Thus suppose A (fig. 119), to represent the north-east

portion of Australia, and _b c_ the ancient level of the sea, when the

coral reef _d_ was formed. If the land sink so that it is submerged more

and more, the sea must at length stand at the level _e f_, the reef in

the mean time having been enlarged and raised to the point _g_. The

distance between the shore _f_, and the barrier reef _g_, is now much

greater than originally between the shore _c_ and the reef _d_, and the

longer the subsidence continues the farther will the coast of the

mainland recede.

When the first edition of this work appeared in 1831, several years

before Mr. Darwin had investigated the facts on which his theory is

founded, I had come to the opinion that the land was subsiding at the

bottom of those parts of the Pacific where atolls are numerous, although

I failed to perceive that such a subsidence, if conceded, would equally

solve the enigma as to the form both of annular and barrier reefs.

I shall cite the passage referred to, as published by me in 1831:--"It

is a remarkable circumstance that there should be so vast an area in

Eastern Oceanica, studded with minute islands, without one single spot

where there is a wider extent of land than belongs to such islands as

Otaheite, Owhyhee, and a few others, which either have been or are still

the seats of active volcanoes. If an equilibrium only were maintained

between the upheaving and depressing force of earthquakes, large islands

would very soon be formed in the Pacific; for, in that case, the growth

of limestone, the flowing of lava, and the ejection of volcanic ashes,

would combine with the upheaving force to form new land.

"Suppose a shoal, 600 miles in length, to sink fifteen feet, and then to

remain unmoved for a thousand years; during that interval the growing

coral may again approach the surface. Then let the mass be re-elevated

fifteen feet, so that the original reef is restored to its former

position: in this case, the new coral formed since the first subsidence

will constitute an island 600 miles long. An analogous result would have

occurred if a lava-current fifteen feet thick had overflowed the

submerged reef. The absence, therefore, of more extensive tracts of land

in the Pacific, seems to show that the amount of subsidence by

earthquakes exceeds, in that quarter of the globe, at present, the

elevation due to the same cause."[1127]

Another proof also of subsidence derived from the structure of atolls,

was pointed out by me in the following passage in all former editions.

"The low coral islands of the Pacific," says Captain Beechey, "follow

one general rule in having their windward side higher and more perfect

than the other. At Gambia and Matilda islands this inequality is very

conspicuous, the weather side of both being wooded, and of the former

inhabited, while the other sides are from twenty to thirty feet under

water; where, however, they may be perceived to be equally _narrow_ and

well defined. It is on the leeward side also that the entrances into the

lagoons occur; and although they may sometimes be situated on a side

that runs in the direction of the wind, as at Bow Island, yet there are

none to windward." These observations of Captain Beechey accord with

those which Captain Horsburgh and other hydrographers have made in

regard to the coral islands of other seas. From this fortunate

circumstance ships can enter and sail out with ease; whereas if the

narrow inlets were to windward, vessels which once entered might not

succeed for months in making their way out again. The well-known

security of many of these harbors depends entirely on this fortunate

peculiarity in their structure.

"In what manner is this singular conformation to be accounted for? The

action of the waves is seen to be the cause of the superior elevation

of some reefs on their windward sides, where sand and large masses of

coral rock are thrown up by the breakers; but there is a variety of

cases where this cause alone is inadequate to solve the problem; for

reefs submerged at considerable depths, where the movements of the sea

cannot exert much power, have, nevertheless, the same conformation, the

leeward being much lower than the windward side.[1128]

"I am informed by Captain King, that, on examining the reefs called

Rowley Shoals, which lie off the north-west coast of Australia, where

the east and west monsoons prevail alternately, he found the open side

of one crescent-shaped reef, the Imparieuse, turned to the east, and of

another, the Mermaid, turned to the west; while a third oval reef, of

the same group, was entirely submerged. This want of conformity is

exactly what we should expect, where the winds vary periodically.

"It seems impossible to refer the phenomenon now under consideration to

any original uniformity in the configuration of submarine volcanoes, on

the summits of which we may suppose the coral reefs to grow; for

although it is very common for craters to be broken down on one side

only, we cannot imagine any cause that should breach them all in the

same direction. But the difficulty will, perhaps, be removed, if we call

in another part of the volcanic agency--subsidence by earthquakes.

Suppose the windward barrier to have been raised by the mechanical

action of the waves to the height of two or three yards above the wall

on the leeward side, and then the whole island to sink down a few

fathoms, the appearances described would then be presented by the

submerged reef. A repetition of such operations, by the alternate

elevation and depression of the same mass (an hypothesis strictly

conformable to analogy), might produce still greater inequality in the

two sides, especially as the violent efflux of the tide has probably a

strong tendency to check the accumulation of the more tender corals on

the leeward reef; while the action of the breakers contributes to raise

the windward barrier."[1129]

Previously to my adverting to the signs above enumerated of a downward

movement in the bed of the ocean, Dr. MacCulloch, Captain Beechey, and

many other writers, had shown that masses of recent coral had been laid

dry at various heights above the sea-level, both in the Red Sea, the

islands of the Pacific, and in the East and West Indies. After

describing thirty-two coral islands in the Pacific, Captain Beechey

mentioned that they were all formed of living coral except one, which,

although of coral formation, was raised about seventy or eighty feet

above the level of the sea, and was encompassed by a reef of living

coral. It is called Elizabeth or Henderson's Island, and is five miles

in length by one in breadth. It has a flat surface, and, on all sides,

except the north, is bounded by perpendicular cliffs about fifty feet

high, composed entirely of dead coral, more or less porous, honey-combed

at the surface, and hardening into a compact calcareous mass, which

possesses the fracture of secondary limestone, and has a species of

millepore interspersed through it. These cliffs are considerably

undermined by the action of the waves, and some of them appear on the

eve of precipitating their superincumbent weight into the sea. Those

which are less injured in this way present no alternate ridges or

indication of the different levels which the sea might have occupied at

different periods; but a smooth surface, as if the island, which has

probably been raised by volcanic agency, had been forced up by one great

subterraneous convulsion.[1130] At the distance of a few hundred yards

from this island, no bottom could be gained with 200 fathoms of line.

[Illustration: Fig. 120.

Elizabeth, or Henderson's Island.]

It will be seen, from the annexed sketch, communicated to me by

Lieutenant Smith, of the Blossom, that the trees came down to the beach

towards the centre of the island; a break at first sight resembling the

openings which usually lead into lagoons; but the trees stand on a steep

slope, and no hollow of an ancient lagoon was perceived.

Beechey also remarks, that the surface of Henderson's Island is flat,

and that in Queen Charlotte's Island, one of the same group, but under

water, there was no lagoon, the coral having grown up everywhere to one

level. The probable cause of this obliteration of the central basin or

lagoon will be considered in the sequel.

That the bed of the Pacific and Indian oceans, where atolls are

frequent, must have been sinking for ages, might be inferred, says Mr.

Darwin, from simply reflecting on two facts; first, that the efficient

coral-building zoophytes do not flourish in the ocean at a greater depth

than 120 feet; and, secondly, that there are spaces occupying areas of

many hundred thousand square miles, where all the islands consist of

coral, and yet none of which rise to a greater height than may be

accounted for by the action of the winds and waves on broken and

triturated coral. Were we to take for granted that the floor of the

ocean had remained stationary from the time when the coral began to

grow, we should be compelled to assume that an incredible number of

submarine mountains of vast height (for the ocean is always deep, and

often unfathomable between the different atolls) had all come to within

120 feet of the surface, and yet no one mountain had risen above water.

But no sooner do we admit the theory of subsidence, than this great,

difficulty vanishes. However varied may have been the altitude of

different islands, or the separate peaks of particular mountain-chains,

all may have been reduced to one uniform level by the gradual

submergence of the loftiest points, and the additions made to the

calcareous cappings of the less elevated summits as they subsided to

great depths.

_Openings into the lagoons._--In the general description of atolls and

encircling reefs, it was mentioned that there is almost always a deep

narrow passage opening into the lagoon, or into the still water between

the reef and the shore, which is kept open by the efflux of the sea as

the tide goes down.

The origin of this channel must, according to the theory of subsidence

before explained, be traced back to causes which were in action during

the existence of the encircling reef, and when an island or mountain-top

rose within it, for such a reef precedes the atoll in the order of

formation. Now in those islands in the Pacific, which are large enough

to feed small rivers, there is generally an opening or channel in the

surrounding coral reef at the point where the stream of fresh water

enters the sea. The depth of these channels rarely exceeds twenty-five

feet; and they may be attributed, says Captain Beechey, to the aversion

of the lithophytes to fresh water, and to the probable absence of the

mineral matter of which they construct their habitations.[1131]

Mr. Darwin, however, has shown, that mud at the bottom of river-courses

is far more influential than the freshness of the water in preventing

the growth of the polypi, for the walls which inclose the openings are

perpendicular, and do not slant off gradually, as would be the case, if

the nature of the element presented the only obstacle to the increase of

the coral-building animals.

When a breach has thus been made in the reef, it will be prevented from

closing up by the efflux of the sea at low tides; for it is sufficient

that a reef should rise a few feet above low-water mark to cause the

waters to collect in the lagoon at high tide, and when the sea falls, to

rush out at one or more points where the reef happens to be lowest or

weakest. This event is strictly analogous to that witnessed in our

estuaries, where a body of salt water accumulated during the flow issues

with great velocity at the ebb of the tide, and scours out or keeps open

a deep passage through the bar, which is almost always formed at the

mouth of a river. At first there are probably many openings, but the

growth of the coral tends to obstruct all those which do not serve as

the principal channels of discharge; so that their number is gradually

reduced to a few, and often finally to one. The fact observed

universally, that the principal opening fronts a considerable valley in

the encircled island, between the shores of which and the outer reef

there is often deep water, scarcely leaves any doubt as to the real

origin of the channel in all those countless atolls where the nucleus of

land has vanished.

_Size of atolls and barrier reefs._--In regard to the dimensions of

atolls, it was stated that some of the smallest observed by Beechey in

the Pacific were only a mile in diameter. If their external slope under

water equals upon an average an angle of 45 degrees, then would such an

atoll at the depth of half a mile, or 2640 feet, have a diameter of two

miles. Hence it would appear that there must be a tendency in every

atoll to grow smaller, except in those cases where oscillations of level

enlarge the base on which the coral grows by throwing down a talus of

detrital matter all round the original cone of limestone.

Bow Island is described by Captain Beechey as seventy miles in

circumference, and thirty in its greatest diameter, but we have seen

that some of the Maldives are much larger.

As the shore of an island or continent which is subsiding will recede

from a coral reef at a slow or rapid rate according as the surface of

the land has a steep or gentle slope, we cannot measure the thickness of

the coral by its distance from the coast; yet, as a general rule, those

reefs which are farthest from the land imply the greatest amount of

subsidence. We learn from Flinders, that the barrier reef of

north-eastern Australia is in some places seventy miles from the

mainland, and it should seem that a calcareous formation is there in

progress 1000 miles long from north to south, with a breadth varying

from twenty to seventy miles. It may not, indeed, be continuous over

this vast area, for doubtless innumerable islands have been submerged

one after another between the reef and mainland, like some which still

remain, as, for example, Murray's Islands, lat. 9 degrees 54 minutes S.

We are also told that some parts of the gulf inclosed within a barrier

are 400 feet deep, so that the efficient rock-building corals cannot be

growing there, and in other parts of it islands appear encircled by

reefs.

It will follow as one of the consequences of the theory already

explained that, provided the bottom of the sea does not sink too fast to

allow the zoophytes to build upwards at the same pace, the thickness of

coral will be great in proportion to the rapidity of subsidence, so that

if one area sinks two feet while another sinks one, the mass of coral in

the first area will be double that in the second. But the downward

movement must in general have been very slow and uniform, or where

intermittent, must have consisted of a great number of depressions, each

of slight amount, otherwise the bottom of the sea would have been

carried down faster than the corals could build upwards, and the island

or continent would be permanently submerged, having reached a depth of

120 or 150 feet, at which the effective reef-constructing zoophytes

cease to live. If, then, the subsidence required to account for all the

existing atolls must have amounted to three or four thousand feet, or

even sometimes more, we are brought to the conclusion that there has

been a _slow_ and _gradual_ sinking to this enormous extent. Such an

inference is perfectly in harmony with views which the grand scale of

denudation, everywhere observable in the older rocks, has led geologists

to adopt in reference to upward movements. They must also have been

gradual and continuous throughout indefinite ages to allow the waves and

currents of the ocean to operate with adequate power.

The map constructed by Mr. Darwin to display at one view the

geographical position of all the coral reefs throughout the globe is of

the highest geological interest (see above, p. 351.), leading to

splendid generalizations, when we have once embraced the theory that all

atolls and barrier reefs indicate recent subsidence, while the presence

of fringing reefs proves the land to be stationary or rising. These two

classes of coral formations are depicted by different colors; and one of

the striking facts brought to light by the same classification of coral

formations is the absence of active volcanoes in the areas of

subsidence, and their frequent presence in the areas of elevation. The

only supposed exception to this remarkable coincidence at the time when

Mr. Darwin wrote, in 1842, was the volcano of Torres Strait, at the

northern point of Australia, placed on the borders of an area of

subsidence; but it has been since proved that this volcano has no

existence.

We see, therefore, an evident connection, first, between the bursting

forth every now and then of volcanic matter through rents and fissures,

and the expansion or forcing outwards of the earth's crust, and,

secondly, between a dormant and less energetic development of

subterranean heat, and an amount of subsidence sufficiently great to

cause mountains to disappear over the broad face of the ocean, leaving

only small and scattered lagoon islands, or groups of atolls, to

indicate the spots where those mountains once stood.

On a review of the differently-colored reefs on the map alluded to, it

will be seen that there are large spaces in which upheaval, and others

in which depression prevails, and these are placed alternately, while

there are a few smaller areas where movements of oscillation occur. Thus

if we commence with the western shores of South America, between the

summit of the Andes and the Pacific (a region of earthquakes and active

volcanoes), we find signs of recent elevation, not attested indeed by

coral formations, which are wanting there, but by upraised banks of

marine shells. Then proceeding westward, we traverse a deep ocean

without islands, until we come to a band of _atolls_ and encircled

islands, including the Dangerous and Society archipelagoes, and

constituting an area of subsidence more than 4000 miles long and 600

broad. Still farther, in the same direction, we reach the chain of

islands to which the New Hebrides, Salomon, and New Ireland belong,

where fringing reefs and masses of elevated coral indicate another area

of upheaval. Again, to the westward of the New Hebrides we meet with the

encircling reef of New Caledonia and the great Australian barrier,

implying a second area of subsidence.

The only objection deserving attention which has hitherto been advanced

against the theory of atolls, as before explained (p. 759.), is that

proposed by Mr. Maclaren.[1132] "On the outside," he observes, "of coral

reefs very highly inclined, no bottom is sometimes found with a line of

2000 or 3000 feet, and this is by no means a rare case. It follows that

the reef ought to have this thickness; and Mr. Darwin's diagrams show

that he understood it so. Now, if such masses of coral exist under the

sea, they ought somewhere to be found on _terra firma_; for there is

evidence that all the lands yet visited by geologists, have been at one

time submerged. But neither in the great volcanic chain, extending from

Sumatra to Japan, nor in the West Indies, nor in any other region yet

explored, has a bed or formation of coral even 500 feet thick been

discovered, so far as we know."

When considering this objection, it is evident that the first question

we have to deal with is, whether geologists have not already discovered

calcareous masses of the required thickness and structure, or precisely

such as the upheaval of atolls might be expected to expose to view? We

are called upon, in short, to make up our minds both as to the internal

composition of the rocks that must result from the growth of corals,

whether in lagoon islands or barrier reefs, and the external shape which

the reefs would retain when upraised gradually to a vast height,--a task

by no means so easy as some may imagine. If the reader has pictured to

himself large masses of entire corals, piled one upon another, for a

thickness of several thousand feet, he unquestionably mistakes

altogether the nature of the accumulations now in progress. In the first

place, the strata at present forming very extensively over the bottom of

the ocean, within such barrier reefs as those of Australia and New

Caledonia, are known to consist chiefly of horizontal layers of

calcareous sediment, while here and there an intermixture must occur of

the detritus of granitic and other rocks brought down by rivers from the

adjoining lands, or washed from sea-cliffs by the waves and currents.

Secondly, in regard to atolls, the stone-making polypifers grow most

luxuriantly on the outer edge of the island, to a thickness of a few

feet only. Beyond this margin broken pieces of coral and calcareous sand

are strewed by the breakers over a steep seaward slope, and as the

subsidence continues the next coating of live coral does not grow

vertically over the first layer, but on a narrow annular space within

it, the reef, as was before stated (p. 761), constantly contracting its

dimensions as it sinks. Thirdly, within the lagoon the accumulation of

calcareous matter is chiefly sedimentary, a kind of chalky mud derived

from the decay of the softer corallines, with a mixture of calcareous

sand swept by the winds and waves from the surrounding circular reef.

Here and there, but only in partial clumps, are found living corals,

which grow in the middle of the lagoon, and mixed with fine mud and

sand, a great variety of shells, and fragments of testacea and

echinoderms.

We owe to Lieutenant Nelson the discovery that in the Bermudas the

calcareous mud resulting from the decomposition of the softer corallines

is absolutely undistinguishable when dried from the ordinary white chalk

of Europe,[1133] and this mud is carried to great distances by currents,

and spread far and wide over the floor of the ocean. We also have

opportunities of seeing in upraised atolls, such as Elizabeth Island,

Tonga, and Hapai, which rise above the level of the sea to heights

varying from ten to eighty feet, that the rocks of which they consist do

not differ in structure or in the state of preservation of their

included zoophytes and shells from some of the oldest limestones known

to the geologist. Captain Beechey remarks that the dead coral in

Elizabeth Island is more or less porous and honeycombed at the surface,

and hardening into a compact rock which has the fracture of _secondary

limestone_.[1134]

The island of Pulo Nias, off Sumatra (see Map, fig. 39. p. 351), which

is about 3000 feet high, is described by Dr. Jack as being overspread by

coral and large shells of the _Chama (Tridacna) gigas_, which rest on

quartzose and arenaceous rocks, at various levels from the sea-coast to

the summit of the highest hills.