SECONDARY ROCKS.
_No. 4. The Wealden._
“The works of the Lord are great, sought out of all them that have
pleasure therein.”—DAVID.
Lying immediately between the oolite and the chalk, is a small formation
of fresh water, and not of marine deposit, to which the term Wealden has
been given. This name has been given to it because it has been found
developed chiefly in the Wealds, or Wolds,[98] of Sussex, Surrey, and
Kent; and to Dr. Mantell belongs the honour of investigating this
singularly interesting formation, and of giving us its history, after
months of patient research and laborious toil conducted on the spot,
just as Hugh Miller has become the historian and explorer of the Old Red
Sandstone of Cromarty. But although the Wealden is small when compared
with the vast extent of some other formations, previously or
subsequently added to the material of this “great globe’s” crust, it
possesses unusual interest on account of the strange organic remains
that are found in it, and of the evidence which these remains supply of
vast changes in the conditions and characters of the living beings,
found at that period roaming at large in the once tropical swamps of the
Wealden.
The Wealden is almost if not wholly of fresh water origin; and a word or
two on the formation of the deltas of great rivers, now going on in
various parts of the world, will help us rightly to appreciate the
character of this formation. It is seldom, some one remarks, that we
“can catch a mountain in process of making,” and hence we have much
difficulty in arriving at definite ideas concerning the times that the
sedimentary rocks occupied in their deposit. But we _can catch_ deltas
in the process of manufacture,—the deltas of the Nile, the Mississippi,
the Amazon, and other huge rivers that pour down, not their “_golden
streams_,” but their muddy accumulations, gathered from the mountain
sides whose slopes they wash into the great ocean basin waiting to
receive them. “All the rivers run into the sea, yet the sea is not
full.”
These deltas,—for we wish to explain as we go along, and would rather
fall into the error of explaining where there is no necessity, than of
leaving one word that might prove a stumbling-block unexplained,—these
deltas are all the mouths, (_les embouchères_,) of _oceanic_ rivers,
that is, of rivers that pursue their impetuous course towards their
native ocean bed; and the character of these deltas necessarily varies
with the character of the coast through which they pursue the _un_even
“tenor of their way.” As the level of the sea is approached, the
rapidity of the mountain stream is necessarily checked. No longer
dashing down steep mountain precipices, as it did in the heyday of its
youth, it finds itself grown into a majestic breadth and depth; and as
it nears its maternal home, leaving the high land of its origin far
behind, it traverses with slow and measured pace the slightly descending
planes by which it falls into the ocean. This gradual process enables it
to deposit on each side the alluvial soil, and decayed vegetable matter,
and so on, that have been held by it in suspension during its rapid
progress; and as the current slackens still more as it approaches its
final destiny, portions of land gradually rise into view, the results of
these deposits, which from their triangular shape have received the name
of deltas, from their likeness to the Greek letter Δ.
Thus the mouths of the Ganges form a vast breadth of waters, with
intervening islands and strips of land, 200 miles in width. Into this
delta the river Ganges runs laden with the rich spoils of clay, sand,
vegetable matter, &c., gathered from the Himalaya Mountains, and thus
those dismal-looking islands have been formed in the mouth of this
river, that have become the home of tigers, crocodiles, &c.
In North America, that “father of waters,” the Mississippi, sometimes
called the Missouri, runs through a glorious valley of unexhausted and
inexhaustible wealth of 3,000 miles, and runs out into the sea at least
fifty miles, while its currenmiles further. “Like all other great
rivers, the Mississippi does not empty itself into the sea in one
continuous channel, but in a great variety of arms or mouths, which
intersect in sluggish streams the great alluvial delta, which is formed
by the perpetual deposit of the immense volume of water which rolls into
the ocean. Between these mouths of the river a vast surface, half land,
half water, from 50 to 100 miles in width, and 300 in length, fringes
the whole coast; and there the enormous mass of vegetable matter
constantly brought down by the Mississippi is periodically deposited. A
few feet are sufficient to bring it above the level of the water, except
in great floods; and as soon as that is done, vegetation springs up with
the utmost rapidity in that prolific slime. No spectacle can be
conceived so dreary and yet so interesting, as the prospect of these
immense alluvial swamps in the course of formation. As far as the eye
can reach, over hundreds of square leagues, nothing is to be seen but
marshes bristling with roots, trunks, and branches of trees. In winter
and spring, when the floods come down, they bring with them an
incalculable quantity of these broken fragments, technically called
logs, which not only cover the whole of this immense semi-marine
territory, but, floating over it, strew the sea for several miles off to
such an extent, that ships have often no small difficulty in making
their way through them. Thus the whole ground is formed of a vast
network of masses of wood, closely packed and rammed together to the
depth of several fathoms, which are gradually cemented by fresh
deposits, till the whole acquires by degrees a firm consistency. Aquatic
birds, innumerable cranes and storks, water serpents, and huge
alligators, people this dreary solitude. In a short time a kind of rank
cane or reed springs up, which, by retarding the flow of the river,
collects the mud of the next season, and so lends its share in the
formation of the delta. Fresh logs, fresh mud, and new crops of cane or
reed, go on for a series of years, in the course of which the
alligators, in enormous multitudes, fix in their new domain, and
extensive animal remains come to mingle with the vegetable deposits.
Gradually, as the soil accumulates and hardens, a dwarfish shrub begins
to appear above the surface; larger and larger trees succeed with the
decay of their more stunted predecessors; and at length, on the scene of
former desolation, the magnificent riches of the Louisianian forest are
reared.”[99]
To this glowing description we might add what we ourselves have
witnessed on the coast of South America, where the great Amazon, the
Orinoco, and the Essequibo, roll their mud-laden waters into the
Atlantic, and form vast accumulations of alluvial deposit all along its
northern coast; indeed, the coast line of all the Guianas of South
America, averaging some five to ten miles in width, and at least 1,000
miles in length,—Venezuela, British Guiana, Surinam, and Cayenne,—are
nothing more than the deposit formed at the base of the mountains by
these and other rivers of smaller note. Buried in this mud are pebbles,
trunks of trees, animal remains, and so on; and if these in process of
time should be elevated and afterwards hardened, or submerged and
pressed into clayey slate or sandy stone, the fauna and the flora of
these deltas would then be brought to light, just as the leaves of
plants are exhibited between the pages of a botanist’s collecting book.
In some such method as this was once formed a delta, now constituting
the Wealden formation in our own country. What is now the south-east of
England, including the Weald clay, the Hastings sand, and the Purbeck
beds of limestone and marls, in short, the greater part of the counties
already named, with part of Dorsetshire, was once the delta of a mighty
river, that so long and so uninterruptedly flowed through this then
uninhabited part of the planet, that its accumulated deposits average
1,000 feet in thickness. We have but to pause over those words—_one
thousand feet thick_;—once mud, or rather fluviatile deposits of mud and
sand, a thousand feet thick in order to receive fresh evidence of the
high antiquity of the globe, and of the recent creation of man. We have
but for a moment to remember that these deposits consist of innumerable
layers of mollusks and crustaceans, a prodigious accumulation of the
bones of reptiles and fishes, and of the trunks, branches, and foliage
of a long extinct vegetable world, all quietly brought down by “the
rivers of waters” of that era, and carefully and without injury
deposited in what were then the bottoms of bays or the rising land of
deltas, in order to appreciate the evidence which this one deposit alone
affords of the immense period of time occupied in its accumulation.
Our next section, the cretaceous division of the secondary rocks,
presents us with an exclusively marine deposit. The Wealden, as we have
said, is a fresh-water deposit. “Many a long and weary journey,” says
Dr. Mantell, “have I undertaken to examine the materials thrown up from
a newly-made well, or the section exposed by recent cuttings on the
roadside, in the hope of obtaining the data by which this problem is now
completely settled.” The data referred to are such as these—the absence
of all ammonites, encrinites, corals, terebratulæ, and other marine
organisms, which form so large a portion of the cretaceous and other sea
deposits.
Here, again, we may anticipate future remarks. It may be thought—by some
it has been roundly asserted—that these _fossils were placed in their
present situations by the deluge_. Without entering into the theological
question, as to the universality or partiality of the Noachian flood,
although, as we shall hereafter see, there is but one opinion on that
subject held by our best geologists, namely, that the deluge recorded in
the Bible was simply the subsidence or submerging of so much of the
earth, _and no more_, as was then inhabited by man, and that so partial
and so limited was its character, and so brief its duration, compared
with those vast geological epochs we have been considering, that there
are no traces in nature of that event at all, _i.e._ that we have no one
single fossil that can be referred to that event,—without, we repeat,
entering upon the investigation of this subject, which will be done in a
subsequent part of this volume, we would merely remark, in reply to this
absurd notion, that the Wealden is evidently an _alluvial_, and not a
_diluvial_ formation; and as these terms are so frequently used as if
they were synonymous, we shall venture upon our old habit of
explanation. An _alluvial_ deposit is formed by the _ordinary_, but a
_diluvial_ deposit by the _extraordinary_ action of water. Thus all the
straths and carses of Scotland, and our English dales or dells, (may not
the remote etymology be _delta_?) are all of alluvial formation; while,
as owing their origin to diluvial, or the violent action of water, we
are to ascribe the heaps of rubbish, gravel, sand and boulders, that are
found in firm compact together.
Thus, if we take a basin of water holding a quantity of earthy matter in
solution, and place it on a quiet table, and allow the earthy matter
gradually to subside, that which is found at the bottom of the basin is
an _alluvial_ formation, deposited by the quiet and ordinary action of
water.
But when, as sometimes here in Royston, a sudden and heavy rain occurs,
when for a while “the windows of heaven” seem opened, and the
surrounding hills pour down their rushing streams through the town,
filling, as unfortunately they do on such occasions, the cellars of our
neighbours in the bottom of the town, with sticks, stones, flint,
gravel, bits of chalk, paper, bones, cloth, and a variety of
intermingled sundries too numerous to mention, and all huddled together
in wild confusion, then is formed in such ill-fated cellars a _diluvial_
deposit, occasioned by the extraordinary action of water.
Now, the Scripture flood (and we may be allowed to say, we are not
trying to explain away the fact of the deluge,[100] nor to weaken the
strength of the Mosaic narrative, but the very contrary) was a most
extraordinary event. Not only were the “windows of heaven opened,” but
the “fountains of the great deep” were broken up, and if it had left any
traces of its action, they would have been of a heterogeneous and
diluvial character; whereas in the Wealden, as elsewhere, the fossils
occur in the most orderly and quiet manner, preserving in many cases
those exquisite forms of beauty which distinguished them during life.
Without entering more fully into details of the fossil remains of this
period, we shall conclude this chapter by a reference to one of the vast
saurians whose remains have been disinterred from the Wealden. Many
years ago Dr. Mantell discovered, in a quarry at Cuckfield in Sussex, a
tooth, which he took up to the Geological Society of London; it was
altogether unlike any tooth he had hitherto found, but yet it was so
common, that the quarrymen had broken many of them up to mend the roads.
The most eminent geologists of the day were puzzled extremely with this
tooth. One thought it belonged to a fish; another, that it belonged to
an unknown herbivorous mammal; and a third, who was right, that it
belonged to a herbivorous reptile. Sir Charles Lyell was at that time
about to visit Paris, and the tooth, and that alone, was shown to
Cuvier, who at once pronounced it to be the tooth of a rhinoceros. In
the process of time other fossil remains were found, portions of jaws,
cervical, dorsal, and caudal vertebræ; and on Cuvier seeing these, with
the magnanimity of a truly great mind, he frankly avowed his error, and
said, “I am entirely convinced of my error in pronouncing it to be the
tooth of a rhinoceros.” Shortly after, Dr. Mantell was fortunate enough
to procure the skeleton of an iguana,[101] and he found that the fossil
teeth found in Tilgate forest bore a close resemblance to the teeth of
the iguana. The teeth of the iguana were found to be small, closely set,
and serrated like the edge of a saw, not so much for crushing victims,
as for champing and grinding its vegetable food; this corresponded
precisely with the fossil teeth found, and after long and careful
deliberation, the name given to this crocodile lizard, and the name
which it retains, was Iguanodon, or the reptile with teeth like the
iguana.
The probable size of the Iguanodon was thirty feet in length, though
probably some exceeded these enormous proportions. Seventy species have
been discovered in the quarries opened at Tilgate forest; and this gives
us some idea of the conspicuous part these mighty creatures once played
in the eras happily before man was an inhabitant of this planet. Why
these remains should generally be found in the same locality we cannot
certainly tell, though the previous extract from Alison may shed some
light on this curious fact; but it appears beyond doubt that particular
spots were selected by these beasts as hospitals and dying places,
where, undisturbed by their enemies, they retired to die unseen.
The drawing on page 195, representing the restored fauna of this period,
that is, inclusive of the Lias, Oolite, and Wealden formations, will not
only illustrate our previous remarks, but enable our readers thoroughly
to appreciate the following vivid description of the life of that remote
era, which we do not like to abridge. Should any feel sceptical as to
whether there were ever such “goings on” in this globe of ours,
especially in our eastern counties, now the resort of tourists and
invalids having no dread of such creatures before their eyes, we ask
them not to reject all this as fable until they have gone to the British
Museum, and in Room 3, and in Wall-case C, they will there see some of
the magnificent specimens, obtained by Dr. Mantell, of these extinct
deinosaurians.[102] On reading this description, it seems quite
justifiable to congratulate ourselves upon the era in which we live.
Strange forms and monsters vast have been in the old time before us, and
their disinterred remains teach us again and again the good and
wholesome lesson of the king of Israel, prefixed as a motto to this
chapter.
“Two of these saurians have more especially attracted attention, in
consequence of their great abundance in a fossil state in our own
country, but they are by no means the only ones known. Of these two, one
was more exclusively a tenant of the deep, while the other was probably
more frequently met with on the mud banks or on the shore. Both were
truly marine in their habits, and both seem to have served as the
representatives of the great Cetacean tribe—the whales, the porpoises,
and other similar animals now existing.
“It is not easy to imagine the conditions of existence of such animals.
We know their form, their proportions, their strange contrivances of
structure, their very skin, and the nature of the food which they
devoured; and yet, knowing with absolute certainty these points, we
hardly dare draw the conclusions which are suggested. I will, however,
venture to offer a sketch of the appearance of the sea and its
inhabitants during this portion of the Reptilian epoch.
“There were then, perhaps, existing on or near the land, some of those
reptiles which I shall describe in the next chapter; and with them were
associated true crocodilians, not much unlike the fresh water gavial
inhabiting the Ganges. These, also, might occasionally swim out to sea,
and be found in the neighbouring shoals.
“But these shoals were alive with myriads of invertebrated animals; and
crowds of sharks hovered about, feeding upon the larger tribes. There
were also numerous other animals, belonging to those remarkable groups
which I have attempted to describe in some detail. Imagine one of these
monstrous animals, a plesiosaurus, some sixteen or twenty feet long,
with a small wedge-shaped crocodilian head, a long, arched, serpent-like
neck, a short compact body, provided with four large and powerful
paddles, almost developed into hands; an animal not covered with
brilliant scales, but with a black slimy skin. Imagine for a moment this
creature slowly emerging from the muddy banks, and, half walking, half
creeping along, making its way towards the nearest water. Arrived at the
water, we can understand from its structure that it was liable to
exhibit greater energy. Unlike the crocodile tribe, however, in all its
proportions, it must have been equally dissimilar in habit. Perhaps,
instead of concealing itself in mud or among rushes, it would swim at
once boldly and directly to the attack. Its enormous neck stretched out
to its full length, and its tail acting as a rudder, the powerful and
frequent strokes of its four large paddles would at once give it an
impulse, sending it through the water at a very rapid rate. When within
reach of its prey, we may almost fancy that we see it drawing back its
long neck as it depressed its body in the water, until the strength of
the muscular apparatus with which this neck was provided, and the great
additional impetus given by the rapid advance of the animal, would
combine to produce a stroke from the pointed head which few living
animals could resist. The fishes, including perhaps even the sharks, the
larger cuttle-fish, and innumerable inhabitants of the sea, would fall
an easy prey to this monster.
“But now let us see what goes on in the deeper abysses of the ocean,
where a free space is given for the operations of that fiercely
carnivorous marine reptile, the ichthyosaurus. Prowling about at a great
depth, where the reptilian structure of its lungs, and the bony
apparatus of the ribs would allow it to remain for a long time without
coming to the air to breathe, we may fancy we see this strange animal,
with its enormous eyes directed upwards, and glaring like globes of
fire. Its length is some thirty or forty feet, its head being six or
eight feet long; and it has paddles and a tail like a shark; its whole
energies are fixed on what is going on above, where the plesiosaurus or
some giant shark is seen devouring its prey. Suddenly striking with its
short but compact paddles, and obtaining a powerful impetus by flapping
its large tail, the monster darts through the water at a rate which the
eye can scarcely follow towards the surface. The vast jaws, lined with
formidable rows of teeth, soon open wide to their full extent; the
object of attack is approached—is overtaken. With a motion quicker than
thought the jaws are snapped together, and the work is done. The
monster, becoming gorged, floats languidly near the surface, with a
portion of the top of its head and its nostrils visible, like an island
covered with black mud, above the water.
[Illustration:
FAUNA OF THE OOLITIC PERIOD, RESTORED.
]
“But a description of such scenes of carnage, enacted at former periods
of the earth’s history, may perhaps induce some of my readers to
question the wisdom that permitted them, and conclude rashly that they
are opposed to the ideas which we are encouraged to form of the goodness
of that Being, the necessary action of whose laws, enforced on all
living beings, gives rise to them. By no means, however, is this the
case. These very results are perfectly compatible with the greatest
wisdom and goodness and even according to our limited views of the
course of nature, they may be shown not to involve any needless
suffering. To us men, constituted as we are, and looking upon death as a
punishment which must be endured, premature and violent destruction
seems to involve unnecessary pain. But such is not the law of nature as
it relates to animal life in general. The very exuberance and abundance
of life is at once obtained and kept within proper bounds by this
rapacity of some great tribes. A lingering death—a natural decay of
those powers which alone enable the animal to enjoy life—would, on the
contrary, be a most miserable arrangement for beings not endowed with
reason, and not assisting each other. It would be cruelty, because it
would involve great and hopeless suffering. Death by violence is to all
unreasoning animals the easiest death, for it is the most instantaneous;
and therefore, no doubt, it has been ordained that throughout large
classes there should be an almost indefinite rate of increase,
accompanied by destruction rapid and complete in a corresponding degree,
since in this way the greatest amount of happiness is ensured, and the
pain of misery and slow decay of the vital powers prevented. All nature,
both living and extinct, abounds with facts proving the truth of this
view; and it would be as unreasonable to doubt the wisdom and goodness
of this arrangement, as it would be to call in question the mutual
adaptation of each part in the great scheme of creation. No one who
examines nature for himself, however superficially, can doubt the
latter; and no one certainly, who duly considers the laws ordained for
the general government of the world, can believe it possible for these
laws to have acted without a system of compensation, according to which
the vital energies of one tribe serve to prepare food for the
development of higher powers in another.”[103]