PRECIOUS STONES.
Diamonds—Diamond Cutting—Rose Diamonds—Brilliants—The
Diamond District in Brazil—Diamond Lavras—The great
Russian Diamond—The Regent—The Koh-i-Noor—Its History—
The Star of the South—Diamonds used for Industrial
Purposes—The Oriental Ruby and Sapphire—The Spinel—The
Chrysoberyl—The Emerald—The Beryl—The Zircon—The Topaz—
The Oriental Turquoise—The Garnet—Lapis Lazuli—The Noble
Opal—Inferior Precious Stones—The Agate-Cutters of
Oberstein—Rock Crystal—The Rock-crystal Grotto of the
Galenstock 477
LIST OF ILLUSTRATIONS.
MAPS.
Of the World, showing the distribution of Volcanoes and the
Districts visited by Earthquakes _to face page_ 60
Of Great Britain, showing the Coal-fields and chief Mining
Districts 400
Of America, showing the Coal-fields and Mineral Districts 410
WOODCUTS.
PAGE
Carboniferous Forest _engraved by_ G. Pearson, _to face
title_
Tabular Geological Profile of
Strata with corresponding _engraved by_ G. Pearson
Fossils 3
Aqueous Strata disturbed by
Igneous Formations ” ” 4
_Ammonites Henleyi_ (Middle _from_ Haughton’s ‘Manual of
Lias) Geology’ 9
Trilobite _from_ Kemp’s ‘Phasis of Matter’ 11
Magnified Eye of Trilobite ” ” 11
_Pterygotus acuminatus_ _from_ Haughton’s ‘Manual of
(Eurypterid) Geology’ 12
_Spirifer princeps_ (Brachiopod) ” ” 12
_Pterichthys Milleri_, restored
(Old Red Sandstone of Scotland) ” ” 14
_Ventriculites_, Fossil Sponge
(Chalk) ” ” 16
_Siphonia costata_, Fossil
Sponge, (Green Sand, ” ”
Warminster) 16
_Encrinus liliiformis_
(Muschelkalk, Germany) ” ” 17
_Pentacrinus briareus_ ” ” 17
_Marsupites ornatus_ (Chalk) ” ” 18
_Turrilites tuberculatum_ ” ” 19
Restored Belemnite ” ” 19
_Ichthyosaurus communis_ ” ” 20
_Plesiosaurus dolichodeirus_
(British Museum—found in the _from_ Haughton’s ‘Manual of
Lias of Street, near Geology’
Glastonbury) 21
_Glyptodon clavipes_ ” ” 25
Diagram illustrating action of _engraved by_ G. Pearson
Syphon 44
Section of an Intermittent Spring ” ” 45
Geysirs of Iceland ” ” 46
Porous Strata, Artesian Well sunk
in the London Basin ” ” 49
Middle and Valley Lake Craters, _from_ Wood’s ‘Australia’ _to face
Mount Gambier, South page_
Australia 53
Extinct Crater of Haleakala _from_ Webb’s ‘Celestial Objects’ 57
Eruption of Vesuvius, Bay of _engraved by_ G. Pearson, _to face
Naples page_ 81
Mud Volcanoes of Trinidad _engraved by_ G. Pearson 94
Great Earthquake at Lisbon _engraved by_ G. Pearson, _to face
page_ 114
Axmouth Landslip _engraved by_ G. Pearson 128
Stalactital Cavern at Aggtelek: _engraved by_ G. Pearson, _to face
the Cave of Borodla page_ 133
Entrance to the Cave of _engraved by_ G. Pearson
Adelsberg 137
Stalactital Cavern in Australia _from_ Wood’s ‘Australia’ 141
Cave under Bonifacio _from_ Forester’s ‘Corsica’ 145
_Leptodirus Höchenwartii_ _engraved by_ G. Pearson 163
The _Proteus anguinus_ ” ” 165
Blind Fish (_Amblyopsis spelæus_) ” ” 168
Indian Rock-cut Temple _engraved by_ G. Pearson, _to face
page_ 178
Rock Temples of Ajunta (general _engraved by_ G. Pearson
view) 182
Lower Glacière of St. Livres _from_ Browne’s ‘Ice Caves’ 193
Ice Streams in the Upper Glacière
of St. Livres ” ” 196
Entrance to the Glacière of St.
Georges ” ” 201
Gallery with Tombs _from_ Northcote and Brownlow’s
‘Roma Sotterranea’ 206
Cave in Dream Lead Mine, near _engraved by_ G. Pearson
Wirksworth, Derbyshire 216
Boring Machine in the Tunnel, _taken from the_ ‘Illustrated
Mont Cenis { }
London News’ _by
permission_ 238
Boring Machine in the Second
Working Gallery, Mont Cenis
Tunnel ” ” 239
Process of Boring _engraved by_ G. Pearson 251
Section of a Lead Mine in _from_ Ure’s ‘Dictionary of
Cardiganshire { Arts, }
Manufacture, and
Mines’. 252
Part of a Colliery laid out in
four panels ” ” 255
General View of Mining _engraved_ by G. Pearson
Operations 257
Tools used by Miners in _from_ Ure’s ‘Dictionary of
Cornwall { Arts, }
Manufactures, and
Mines’ 258
Conveyance of Minerals _engraved by_ G. Pearson
underground 262
Miners descending Shaft in Owen’s
Safety Cage ” ” 265
Timbering of a Mine _from_ Ure’s ‘Dictionary of
{ Arts, }
Manufactures, and Mines’ 258
Transverse Sections of Walled
Drain Galleries ” ” 269
Drainage of a Mine by Adit Levels ” ” 269
Safety Lamp ” ” 280
Gold-washing in Australia _engraved by_ G. Pearson 292
Stamping Mill _from_ Ure’s ‘Dictionary of Arts,
Manufactures, and Mines’ 306
Grinding Mill ” ” 307
The Botallack Mine, Cornwall _engraved by_ G. Pearson 317
St. Michael’s Mount, Cornwall ” ” 333
Blast Furnace _from_ Ure’s ‘Dictionary of Arts,
Manufactures, and Mines’ 352
Pecopteris adiantoides _from_ Haughton’s ‘Manual of
Geology’ 391
Sphenopteris affinis ” ” 391
Lepidodendron elegans ” ” 392
Asterophyllites comosa ” ” 392
Sigillaria oculata ” ” 392
Calamites nodosus ” ” 393
Coalbeds rendered available by _from_ ‘Our Coal and Our Coal Pits’
elevation, 397
Section of Coal-field south of { _from_ Ure’s ‘Dictionary of }
Malmesbury Arts, Manufactures, and Mines’ 398
Coal-basin of Clackmannanshire ” ” 403
Dudley Coal-field _from_ Howitt’s ‘Visits to
Remarkable Places’ 407
Shipping Coal ” ” 412
Coal Hewers at Work _engraved by_ G. Pearson 415
Pitch Lake of Trinidad _engraved by_ G. Pearson, _to face
page_ 429
Insects and Vegetable _engraved by_ G. Pearson
Substances inclosed in Amber, 452
Penrhyn Slate Quarry, North _engraved by_ G. Pearson, _to face
Wales page_ 469
The following is a list of the full-page illustrations, included in the
foregoing list, all of which, except No. 2, are engraved by G. Pearson:—
1. Carboniferous Forest _to face title_
2. Middle and Valley Lake Craters, Mount
Gambier, South Australia _to face page_ 53
3. Eruption of Vesuvius, Bay of Naples ” 81
4. Great Earthquake at Lisbon ” 114
5. Stalactital Cavern at Aggtelek; the Cave
of Borodla ” 133
6. Indian Rock-cut Temple: Porch of the
Chaitya Cave Temple, Ajunta ” 178
7. Pitch Lake of Trinidad ” 429
8. Penrhyn Slate Quarry, North Wales ” 469
CHAPTER I.
GEOLOGICAL REVOLUTIONS.
The Eternal Strife between Water and Fire—Strata of Aqueous Origin—
Tabular View of their Chronological Succession—Enormous Time required
for their Formation—Igneous Action—Metamorphic Rocks—Upheaval and
Depression—Fossils—Uninterrupted Succession of Organic Life.
Geology teaches us that, from times of the remoteness of which the human
mind can form no conception, the surface of the earth has been the scene
of perpetual change, resulting from the action and counter-action of two
mighty agents—water and subterranean heat.
Ever since the first separation between the dry land and the sea took
place, the breakers of a turbulent ocean, the tides and currents, the
torrents and rivers, the expansive power of ice, which is able to split
the hardest rock, and the grinding force of the glacier, have been
constantly wearing away the coasts and the mountains, and transporting
the spoils of continents and islands from a higher to a lower level.
During our short historical period of three or four thousand years, the
waters, in spite of their restless activity and the considerable local
changes effected by their means, have indeed produced no marked
alteration in the great outlines of the sea and land; but when we
consider that their influence has extended over countless ages, we can
no longer wonder at the enormous thickness of the stratified rocks of
aqueous origin which, superposed one above the other in successive
layers, constitute by far the greater part of the earth-rind.
Our knowledge of these sedimentary formations is indeed as yet but
incomplete, for large portions of the surface of the globe have never
yet been scientifically explored; but a careful examination and
comparison of the various strata composing the rocky foundations of
numerous countries, have already enabled the geologist to classify them
into the following chronological systems or groups, arranged in an
ascending series, or beginning with the oldest.
1. Laurentian, named from its discovery northward of the River St.
Lawrence in Canada.
2. Cambrian } These three groups owe their name to their
3. Silurian } occurrence in Wales and Devonshire,
4. Devonian } where they were first scientifically explored.
5. Carboniferous. In this group the most important coal-fields are
found.
6. Permian, from the Russian province of Permia.
7. Triassic.
8. Lias.
9. Oolite.
10. Cretaceous.
11. Tertiary: subdivided into Eocene, Miocene, and Pliocene.
12. Recent marine and lacustrine strata.
Each of these systems consists again of numerous sections and alternate
layers, sometimes of marine, sometimes of freshwater formation, the mere
naming of which would fill several pages.
When we reflect that the Laurentian system alone has a thickness of
30,000 feet; that many of the numerous subdivisions of the Triassic or
Oolitic group are 600, 800, or even several thousand feet thick, and
that each of these enormous sedimentary formations owes its existence to
the disintegration of pre-existing mountain masses—we can form at least
a faint notion of the enormous time which the whole system required for
its completion.
TABULAR GEOLOGICAL PROFILE.
STRATA CHARACTERISTICS
FOSSIL REMAINS
+--------+--------+------------------------
T { 1. RECENT DEPOSITS | | | 1. RECENT DEPOSITS
E { ------------------- | | |
R { 2. PLIOCENE | I | I |
T -{ ------------------- | | | _Irish Elk._
I { 3. MIOCENE | L | L |
A { ------------------- | | |
R { 4. EOCENE | L | L |
Y ------------------- + | |------------------------
{ | U | U | 2. PLIOCENE.
{ | | | _Mastodon._
{ 5. CRETACEOUS | S | S |
{ } | |------------------------
{ --------------------+ T | T | 3. MIOCENE.
{ | | |
S { | R | R | (1) _Cerithium._
E { | | | (2) _Segnoia._
C { | A | A |------------------------
O { | | | 4. EOCENE.
N -{ | T | T |
D { | | | (1) _Nummulites._
A { 6. OOLITIC | I | I | (2) _Natica._
R { | | |------------------------
Y { | O | O | 5. CRETACEOUS.
{ | | |
{ | N | N | (1) _Inoceramus._
{ ------------------- | | | (2) _Turrilites._
{ 7. LIAS | | | (3) _Pecten._
{ | | | (4) _Hamites._
{ ------------------- + | +------------------------
{ 8. TRIASSIC | | | 6. OOLITIC.
{ | | |
{ | | | (1) _Pholadomya._
{ ------------------- + | | (2) _Trigonia._
{ 9. PERMIAN | | | (3) _Mantellia._
{ | | | (4) _Nerinæa._
{ ------------------- + | +------------------------
{ | | | 7. LIAS.
{ | | |
{ | | | (1) _Icthyosaurus._
{ | | | (2) _Ammonites._
{ | | +------------------------
{ 10. CARBONIFEROUS | | | 8. TRIASSIC.
{ | | |
{ | | | (1) _Labyrinthodon._
{ | | | (2) _Encrinus._
{ | | +------------------------
{ | | | 9. Permian.
{ ------------------- + | |
{ | | | (1) _Bakewellia._
{ | | | (2) _Productus._
{ | I | I | (3) _Palæoniscus._
{ + | +------------------------
{ 11. DEVONIAN | L | L | 10. CARBONIFEROUS.
{ | | |
{ | L | L | (1) _Goniatites._
{ | | | (2) _Lepidodendron._
{ | L | I | (3) _Calamites._
{ ------------------- + | +------------------------
P { | U | U | 11. DEVONIAN.
R { | | |
I { | S | S | _Pterichthys._
M -{ | | +------------------------
A { 12. SILURIAN | T | T | 12. SILURIAN.
R { | | |
Y { | R | R | (1) _Strophomena._
{ | | | (2) _Lingula._
{ | A | A | (3) _Pentamerus._
{ | | | (4) _Calymene._
{ ------------------- + T | T +------------------------
{ | | | 13. CAMBRIAN.
{ | I | I |
{ 13. CAMBRIAN | | | _Oldhamia._
{ | O | O +------------------------
{ ------------------- + | | 14. LAURENTIAN.
{ 14. LAURENTIAN | N | N |
{ | | | _Eozoon._
--------------------+--------+--------+------------------------
Had the levelling power of water never met with an antagonistic force,
there can be no doubt that the last remains of the dry land, supposing
it could ever have risen above the ocean, must long since have been
swept into the sea. But while water has been constantly tending to
reduce the irregularities of the earth’s surface to one dull level, the
expansive force of subterranean heat has been no less unceasingly active
in
restoring the unevenness of the external crust by the ejection or
protrusion of new masses of stone (porphyry, trachyte, basalt, lava,
&c.), and by the consequent disturbance, in a variety of ways, of the
stratified rocks.
[Illustration:
AQUEOUS STRATA DISTURBED BY IGNEOUS FORMATIONS.
B C D, aqueous strata, originally horizontal, raised by protrusion of
A, granitic rock.
]
Plutonic and volcanic eruptions and upheavings, in their reaction
against the levelling tendencies of water, have in many places deranged,
broken, fractured, contorted, or raised strata deposited in horizontal
layers at the bottom of the sea, or of large inland lakes. Sometimes a
huge mass of crystalline rock, glowing from the furnaces of the deep,
has, by its irresistible expansion, slowly forced its way through the
superincumbent sedimentary formations, which, yielding to the pressure
from below, now form vast mountain slopes, or vertical rock walls, or
have even been so totally inverted that strata of a more ancient
formation now overlie those of more modern date, and excite the wonder
of the puzzled geologist.
Sometimes, also, volcanic eruptions, repeated through a long lapse of
ages and constantly accumulating lavas and cinders, have at length piled
up large islands, such as Iceland or Madeira, which now raise their
summits thousands of feet above the ocean.
But subterranean fire, and its assistant, steam, have not only produced
vast mechanical changes; they have also been the frequent causes of
great chymical metamorphoses in the rocks subjected to their action. To
the calcining, decomposing, and vapour-generating effects of heat, we
trace the origin of the marble of Carrara, of alabaster, of gypsum, and
all those various species of stone which geologists include under the
name of metamorphic rocks.
Besides the more paroxysmal and violent revolutions resulting from the
action of subterranean fire, we find that the earth-rind has at all
times been subject to slow oscillatory movements of upheaval and
subsidence, frequently alternating on the same spot with long periods of
rest. The greater part of the actual dry land has been deep sea, and
then again land and ocean many times in succession; and doubtless the
actual sea bottom would exhibit similar alternations were we able to
explore it. The same materials have repeatedly been exposed to all these
changes—now raised or poured out by subterranean fires, and then again
swept away by the waters; now changed from solid rock into sand and mud,
and then again converted, by pressure or heat, into solid rock. Thus the
history of the earth-rind opens to us a vista into time no less grand
and magnificent than the vista into space afforded by the contemplation
of the starry heavens.
The oldest and the newest stratified rocks are composed of the same
mineral substances; for clay, sandstone, and limestone occur in the
Silurian and in the Carboniferous formation; in the Cretaceous and
Triassic systems; in the Tertiary and in the Alluvial deposits, which
have immediately preceded the present epoch.
Where then, it may be asked, does the geologist find a chronological
guide to lead him through the vast series of strata which, in the course
of countless ages, have been deposited in the water? How is he able to
distinguish the boundaries of the various periods of creation? Where are
the precise indications which enable him to decipher the enigmas which
the endless feuds of fire and water have written in the annals of our
globe?
The fossil remains of animals and plants wonderfully furnish the
guidance which he needs. The corals and shells, the ferns and conifera,
the teeth and bones found in the various strata of the earth-rind are
the landmarks which point out to him his way through the labyrinth of
the primitive ages of our globe, as the compass directs the mariner over
the pathless sea. Every leading fossil has its fixed chronological
character, and thus the age of the formation in which it occurs may be
ascertained, and its place determined in the geological scale. It would,
however, be erroneous to suppose that each successive formation has been
the seat of a totally distinct creation, and that the organic remains
found in one particular stratum are separated by an impassable barrier
from those which characterise the preceding or following sedimentary
deposits.
As on the surface of the earth or along the shores of the sea, each land
or each coast has not only its peculiar plants or animals, but also
harbours many of the organic forms of the neighbouring countries or
conterminous shores; as the tropical organisations gradually pass into
those of the temperate zones, and these again merge into those of the
polar regions, so also the stream of life has from the first flowed
uninterruptedly, in gradually changing forms, through every following
age. New genera and species have arisen, and others have disappeared,
some after a comparatively short duration, others after having outlasted
several formations; but every extinct form has but made way for others,
and thus each period has not only witnessed the decay of many previously
flourishing genera and species, but has also marked a new creation.
No doubt the numerous local disturbances above mentioned have frequently
broken the chain of created beings; but a gradual progress from related
to related forms, a continuous development from lower to more highly
organised species, genera, orders, and classes, has from the beginning
been the general and constant law of organic life. Universal
destructions of existing forms, revolutions covering the whole surface
of the earth with ruin, have most assuredly never occurred in the annals
of our globe.
Nor must it be supposed that the whole scale of sedimentary formations
is to be found superimposed in one spot; for as in our times new strata
are chiefly growing at the mouths of rivers, or where submarine currents
deposit at the bottom of the ocean the fine mud or sand which is
conveyed into the sea by the disintegration of distant mountain chains,
so also from the beginning each stratum could only have been deposited
in similar localities; and while it was slowly increasing, and not
seldom acquiring colossal dimensions in some parts of the globe, others
remained comparatively but little altered, until new oscillatory
movements produced a change in their former position, and opening new
paths to the rolling waters, here set bounds to the progress of one
formation, and there favoured the deposition of another.
A complete study of all the various transformations by fire or water
which the surface of our earth has undergone would require an elaborate
treatise of geology, and lies far beyond the scope or the pretensions of
a popular volume which is chiefly devoted to the description of caves
and mines. But I should be neglecting some of the most interesting
features of the subterranean world, were I to omit all mention of the
fossils imbedded in its various strata; of its internal heat; of the
upheavals and subsidences which have played so conspicuous a part in the
history of the earth-rind, and are still proceeding at the present day;
of the water percolating or flowing beneath the earth’s crust, and
finally of the volcanoes and earthquakes, which prove to us that the
ancient subterranean fires, far from being extinct, are still as
powerful as ever in remodelling its surface.
CHAPTER II.
FOSSILS.
General Remarks—Eozoon Canadense—Trilobites—Brachiopods—Pterichthys
Milleri—Oldest Reptiles—Wonderful Preservation of Colour in Petrified
Shells—Primæval Corals and Sponges—Sea-lilies—Orthoceratites and
Ammonites—Belemnites—Ichthyosaurus and Plesiosaurus—Pterodactyli—
Iguanodon—Tertiary Quadrupeds—Dinotherium—Colossochelys Atlas—
Megatherium—Mylodon—Glyptodon—Mammoth—Mastodon—Sivatherium Giganteum—
Fossil Ripple-marks, Rain-drops, and Footprints—Harmony has reigned
from the beginning.
The fossil remains of plants and animals, which have successively
flourished, and passed away since the first dawn of organic life, occupy
a prominent place among the wonders of the subterranean world. A medal
that has survived the ruin of empires is no doubt a venerable relic, but
it seems to have been struck but yesterday when compared with a shell or
a leaf that has been buried millions of years ago in the drift of the
primeval ocean, and now serves the geologist as a waymark through the
past epochs of the earth’s history.
[Illustration: AMMONITES HENLEYI (MIDDLE LIAS).]
If we examine the condition in which the fossils have been preserved in
the strata successively deposited on the surface of our globe, we find
that in general only parts of the original plant or animal have escaped
destruction, and in these fragments also the primitive substance has
often been replaced by other materials, so that only their form or their
impression has triumphed over time. While soft and delicate textures
have either been utterly swept away, or could only be preserved under
the rarest circumstances (as, for instance, the insects and flowers
inclosed in amber), a greater degree of hardness or solidity naturally
gave a better chance of escaping destruction. Thus among plants the most
frequent fossil-remains are furnished by stems, roots, branches, fruit-
stones, leaves; and, among animals, by corals, shells, calcareous
crusts, teeth, scales, and bones. But the few memorials that have thus
survived the lapse of ages enable us to form some idea of the multitudes
that have entirely perished; and the petrified shell of the Ammonite, or
the jointed arms of the Encrinite, are proofs of the existence of the
world of tiny beings which served them for their nourishment and have
been utterly swept away. If we consider that the number of all the known
species of fossil plants hardly amounts to 3,000, while the Flora of the
present day, as far as it has been examined by systematical botanists,
numbers at least 250,000 species; that the host of living insects is
probably still more numerous, although not much more than 1,500 extinct
species of this class are known to us; and that, finally, the remains of
all the extinct crustaceous fishes, reptiles, and warm-blooded animals
are far outnumbered by the species actually living—we may form some idea
of the vast multitudes that have left no trace behind, and whose total
loss will for ever confine within narrow limits our knowledge of the
past phases of organic creation. This loss appears still greater when we
consider the enormous extent of time during which the fossils known to
us have successively existed, and that a part only of the comparatively
small number of the orders, genera, and species to which they belong
existed at one and the same epoch. But as, owing to the hard texture and
mode of life which are so eminently favourable for the preservation of
shells, we have been enabled to collect about 11,000 fossil species, a
number not much inferior to that of the molluscs of the present day, we
may justly conclude that the more perishable forms of life, of which,
consequently, fewer vestiges have been preserved, were comparatively as
numerous, and that ever since the first dawn of organic life our earth
has borne an immense variety of plants and animals.
Though comparatively but few species have been preserved, yet sometimes
the accumulation of fossil remains is truly astonishing. In the
carboniferous strata we not seldom find more than one hundred beds of
coal interstratified with sandstones, shales, and limestones, and
extending for miles and miles in every direction. How luxuriant must
have been the growth of the forests that could produce masses such as
these, and what countless multitudes of herbivorous insects must have
fed upon their foliage or afforded food to carnivorous hordes scarcely
less numerous than themselves! The remains of corals, encrinites, and
shells often form the greater part of whole mountain ranges, and, what
is still more remarkable, mighty strata of limestone or flint are not
seldom almost entirely composed of the aggregated remains of
microscopical animals.
After these remarks on fossils in general, I will now briefly point out
some of the most striking of the species so preserved to us as they
successively appeared upon the stage of life.
In the Lower Laurentian Rocks, the most ancient strata known, only one
fossil has hitherto been found. The _Eozoon canadense_, as it has been
called, belonged to the Rhizopods, which occupy about the lowest grade
in the scale of animal existence. Its massive skeletons, composed of
innumerable cells, would seem to have extended themselves over submarine
rocks, their base upwards of twelve inches in width and their thickness
from four to six inches. Such is the antiquity of the Eozoon that the
distance of time which separated it from the Trilobites of the Cambrian
formation may be equal to the vast period which elapsed between these
and the Tertiary ages. In other words, it is beyond our imagination to
conceive.
[Illustration: TRILOBITE.]
[Illustration: MAGNIFIED EYE OF TRILOBITE.]
In the next following Cambrian formation we find, besides some zoophytes
and shells, a number of Trilobites, which, however, appear to have been
most abundant in the Silurian seas, where they probably swarmed as
abundantly as the crabs and shrimps in the waters of the present age.
Few fossils are more curious than these strange crustaceans, which so
widely differ from their modern relatives. The jointed carapace is
divided into three lobes, the middle prominent one forming the axis of
the body, while the lateral ones were free appendages, under which the
soft membranaceous swimming feet were concealed. Large eyes, resembling
those of a dragon-fly, projected from the odd crescent-shaped head, and,
being composed of many hundred spherical facets, commanded a wide view
of the horizon. Provided with such complicated organs of vision, the
helpless animal could betimes perceive the approaching enemy, or more
easily espy its prey, consisting, most likely, of the smaller marine
annelides or molluscs. From the structure of these remarkable eyes we
may conclude that the waters of the old Cambrian or Silurian Ocean were
as limpid as those of the present seas, and that the natural relations
of light to the eye and of the eye to light cannot have greatly changed
since that period. Many, if not all, of the Trilobites were capable of
rolling themselves up into a ball, like wood-lice; and accordingly it is
found that in many of them the contour of the head and tail is so
constructed that they fit accurately when rolled up. Most probably the
Trilobites either swam in an inverted position, the belly upwards, or
crawled slowly along at the bottom of the shallow coast waters, where
they lived gregariously in vast numbers.
[Illustration: PTERYGOTUS ACUMINATUS (EURYPTERID).]
[Illustration: SPIRIFER PRINCEPS (BRACHIOPOD).]
Contemporaneous with the Trilobites were the Eurypterids, which vary
from one foot to five or six feet in length. One of the most striking
characteristics of this remarkable order of crustaceans is the
formidable pair of pincers with which they were armed. As their whole
structure shows them to have been active swimmers, they must have made
considerable havoc among the smaller fry of the Devonian and Silurian
seas.
Then also abounded in hundreds of species the Brachiopods, a class of
molluscs now but feebly represented by a scanty remnant. The greater
part of the interior of the shell, consisting of two unequal valves, is
occupied with branching arms, furnished with cilia, which cause a
constant current to flow towards the mouth of the mollusc, and thus
provide for its nourishment. The arms, as in the family of the
Spiriferidæ, are sometimes supported by calcareous skeletons, arranged
like loops or spirals.
Some Brachiopods are attached to stones, like oysters; in others the
larger valve is perforated, and a sinewy kind of foot, passing through
the aperture, serves as a holdfast to the animal.
Most of these helpless creatures did not survive the Carboniferous
period, but the Terebratulæ, which still have their representatives in
the modern seas, existed even then, so that their genealogical tree may
justly boast of a very high antiquity.
The fishes, of which the oldest known specimen has been found in the
Upper Silurian group (Lower Ludlow), become more frequent in the next
following Devonian epoch, where they appear in a variety of wonderful
forms, widely different from those of the present day. While in nearly
all the existing fishes the scales are flexible, and generally either of
a more or less circular form (cycloid), as in the salmon, herring,
roach, &c., or provided with comb-like teeth, projecting from the
posterior margin (ctenoid), as in the sole or perch, the fishes of the
Devonian, Permian, and Carboniferous periods were decked with hard bony
scales, either covered with a brilliant enamel, as in our sturgeons
(ganoid), and arranged in regular rows, the posterior edges of each
slightly overlapping the anterior ones of the next, or irregular in
their shape, and separately imbedded in the skin (placoid), as in the
sharks and rays of the present day. With rare exceptions their skeleton
was cartilaginous; but the less perfect ossification of their bones was
amply compensated by the solid texture of their enamelled coat of mail,
which afforded them a better protection against enemies and injuries
from without than is possessed by any bony-skeletoned fish of our days.
They were, in fact, comparatively as well prepared for a hostile
encounter as an ancient knight in armour, or as one of our modern iron-
plated war ships. One of the most remarkable of these mail-clad Ganoids
was the _Pterichthys Milleri_ of the Old Red Sandstone of Scotland. In
most of our fishes the pectoral fins are but weakly developed; here they
constitute real arms, moved by strong muscles, and resembling the paddle
of the turtle.
[Illustration: PTERICHTHYS MILLERI—RESTORED. (OLD RED SANDSTONE OF
SCOTLAND.)]
Besides the enormous masses of vegetable matter which distinguish the
Carboniferous period, the stone beds of that formation likewise contain
a vast number of animal remains. From the reptiles and fishes down to
the corals and sponges, many new families, genera, and species crowd
upon the scene, while many of the previously flourishing races have
either entirely disappeared, or are evidently declining. Thus the
Trilobites, formerly so numerous, are reduced to a few species in the
Carboniferous period, and vanish towards its close.
In 1847 the oldest known reptiles were found in the coal field of
Saarbrück, in the centre of spheroidal concretions of clay iron-stone,
which not only faithfully preserved the skulls, teeth, and the greater
portions of the skeletons of these ancient lizards, but even a large
part of their skin, consisting of long, narrow, wedge-shaped, tile-like,
and horny scales, arranged in rows. What a lesson for human pride! The
pyramid of the Pharaoh Cheops, reared by the labour of thousands of
slaves, has been unable to preserve his remains from spoliation even for
the short space of a few thousand years, and here a vile reptile has
been safely imbedded in a sarcophagus of iron ore during the vast period
of many geological formations.
Still more recently (1854) other wonders have been brought to light in
the clay iron-stone of Saarbrück. The wing of a grasshopper, with all
its nerves as distinctly marked as if the creature had been hopping
about but yesterday, some white ants or termites (now confined to the
warmer regions of the globe), a beetle, and several cockroaches, give us
some idea of the insects that lived at the time when our coal-beds were
forming. Another highly interesting circumstance, relating to the
fossils of that distant period, is that in several of them the patterns
of their colouring have been preserved. Thus _Terebratula hastata_ often
retains the marks of the original coloured stripes which ornamented the
living shell. In _Aviculopecten sublobatus_ dark stripes alternate with
a light ground, and wavy blotches are displayed in _Pleurotomaria
carinata_. From these facts Professor Forbes inferred that the depth of
the seas in which the Mountain Limestone was formed did not exceed fifty
fathoms, as in the existing seas the Testacea, which have shells and
well-defined patterns, rarely inhabit a greater depth.
The Magnesian Limestone or Permian group is remarkable chiefly for the
vast number of fishes that have been found in some of its members, such
as the marl slate of Durham and the Kupferschiefer, or copper slate, of
Thuringia. From the curved form of their impressions, as if they had
been spasmodically contracted, the fossil fish of the latter locality
are supposed to have perished by a sudden death before they sank down
into the mud in which they were entombed. Probably the copper which
impregnates the stratum in which they occur is connected with this
phenomenon. Mighty volcanic eruptions corrupted the water with poisonous
metallic salts, and destroyed in a short time whole legions of its finny
inhabitants.
[Illustration: VENTRICULITES—FOSSIL SPONGE (CHALK).]
From the earliest ages the corals play a conspicuous part in fossil
history; and as in our days we find them encircling islands and fringing
continents with huge ramparts of limestone, so many an ancient reef, now
far inland, and raised several thousand feet above the level of the sea,
bears witness to the vast terrestrial changes that have taken place
since it was first piled up by the growth of countless zoophytes.
[Illustration: SIPHONIA COSTATA—FOSSIL SPONGE (GREEN SAND, WARMINSTER).]
With regard to the dimensions of the fossil corals we do not find that
any of them exceeded in size their modern relatives; but their
construction was widely different.
The fossil sponges of the primitive seas are likewise very unlike those
of the present day.
Thus in all the ancient strata we find abundant spongidæ with a stony
skeleton, while all the modern sponges possess a horny frame. The
Petrospongidæ, or stone sponges, which have long since disappeared, are
frequently shapeless masses; but a large number are cup-shaped, with a
central tubular cavity, lined, as well as the outer surface, with pores
more or less regularly arranged.
[Illustration:
ENCRINUS LILIIFORMIS.
(Muschelkalk, Germany.)
]
[Illustration: PENTACRINUS BRIAREUS.]
The Crinoids, or Sea-lilies, now almost entirely extinct, were extremely
common in the primeval seas. Unlike our modern sea-stars, to which they
are allies, they did not move about freely from place to place, but were
affixed, like flowers, to a slender flexible stalk, composed of numerous
calcareous joints connected together by a fleshy coat. The Carboniferous
Mountain Limestone is loaded with their remains, and the _Encrinus
liliiformis_ is one of the leading fossils of the Muschelkalk of the
Triassic group. The _Pentacrinus briareus_ is of more modern date, and
occurs in tangled masses, forming thin beds of considerable extent in
the Lower Lias. This beautiful Crinoid, with its innumerable tentacular
arms, appears to have been frequently attached to the drift wood of the
Liassic sea, like the floating barnacles of the present day. In the
still more recent Chalk group is found a remarkable form of star-fish,
the _Marsupites ornatus_, which resembles in all respects the Crinoids,
except that it is not and never was provided with a stem. It seems to
have been rolled lazily to and fro, by the influence of the waves, at
the bottom of the sea, and to have been anchored in its place by the
action of gravity alone.
[Illustration: MARSUPITES ORNATUS. CHALK.]
Of all the changes that have taken place in organic life, none perhaps
are more remarkable than the transformations which the Cephalopod
molluscs have undergone during the various geological eras. In the more
ancient Palæozoic seas flourished the Orthoceratites, or straight-
chambered shells, resembling a nautilus uncoiled. In the Carboniferous
ages the Goniatites acquired their highest development. These shells
were spirally wound, having the lobes of the chambers free from lateral
denticulations or crenatures, so as to form continuous and uninterrupted
outlines.
Both Orthoceratites and Goniatites disappear in the Triassic times, and
are replaced by hosts of Ammonites, which successively flourished in
more than 600 species, and are characterised by an external siphon and
chambers of complicated, often foliated, pattern. This foliated
structure gives a remarkable character to the intersection of the
chamber partitions with the shell, and must have added greatly to the
strength of the shell, which was always delicate and often very
beautiful. The Ammonites, which made their first appearance towards the
end of the Triassic period, abounded in the Oolitic and Cretaceous
periods, and were replaced by new forms before the Tertiary beds were
deposited. Among these we find the _Ancyloceras gigas_, which may be
regarded as an Ammonite partially unrolled, and the _Turrilites
tuberculatus_, which has the form and peculiar symmetry of a univalve
shell.
[Illustration: TURRILITES TUBERCULATUS.]
[Illustration: RESTORED BELEMNITE.]
In several of the older rocks, especially the Lias and Oolite,
Belemnites are frequently met with. These singular dart- or arrow-shaped
fossils were supposed by the ancients to be the thunderbolts of Jove,
but are now known to be the petrified internal bones of a race of
voracious cuttle-fishes, whose importance in the Oolitic or Cretaceous
Seas may be judged of by the frequency of their remains and the 120
species that have been hitherto discovered.
Belemnites two feet long have been found, so that, to judge by
analogies, the animals to which they belonged as cuttle-bones must have
measured eighteen or twenty feet from end to end. Provided with
prehensile hooks on their long arms, and with a formidable parrot-like
bill, these huge creatures must have proved most dangerous antagonists,
even to the well-protected fishes that lived in the same seas. But of
all the denizens of the Mesozoic Ocean none were more powerful than the
large marine or enaliosaurian reptiles, which, flourishing throughout
the whole of the Triassic period, were lords of all they surveyed down
to the end of the Cretaceous epoch. First among these monsters appears
the gigantic Ichthyosaurus, which has been found no less than forty feet
long—a creature half fish, half lizard, and combining, in strange
juxtaposition, the snout of the porpoise, the teeth of the crocodile,
and the paddles of the whale. But the most remarkable of its features is
the eye, surpassing a man’s head in size, and wonderfully adapted for
vision both far and near.
[Illustration: ICHTHYOSAURUS COMMUNIS.]
[Illustration:
PLESIOSAURUS DOLICHODEIRUS.
(British Museum—Found in the Lias of Street, near
Glastonbury.)
]
In the quarries of Caen in Normandy, at Lyme Regis in Dorsetshire, and
particularly at Kloster Banz in Franconia, where the largest known
specimen has been discovered, entire skeletons of the formidable
Ichthyosaurus have been exhumed from the Liassic shale—memorials of the
ages long since past, when lands now far removed from the ocean still
lay at the bottom of the sea, and formed the domain of gigantic lizards.
The enormous jaw-bones of the Ichthyosauri, which in the full-grown
animal could be opened seven feet wide, were armed along their whole
length with powerful conical teeth, showing them to have been
carnivorous, and the half-digested remains of fishes and reptiles found
within their skeletons indicate the precise nature of their food. The
size of the swallowed object proves also that the cavity of the stomach
must have corresponded with the wide opening of the jaws. Thus
powerfully equipped for offensive warfare; excellent swimmers from their
compressed cuneiform trunk, their long broad paddles, and their stout
vertical tail-fin; provided, moreover, with eyes capable of piercing the
dim light of the ocean depths, they must have been formidable indeed to
the contemporaneous fishes.
The Ichthyosaurus was admirably formed for cleaving the waves of an
agitated sea; but the Plesiosaurus was equally well organised for
pursuing its prey in shallow creeks and bays defended from heavy
breakers. Its long swan-like neck no doubt enabled it to drag many a
victim from its hiding-place. While these huge lizards were the terror
of the seas, the Pterodactyles, a race of winged lizards, armed with
long jaws and sharp teeth, hovered in the air. With the exception of the
greatly elongated fifth finger, to which, as well as to the whole length
of the arm and body, the membranous wing or organ of flight was
attached, the fingers of this strange animal were provided with sharp
claws, so that it was probably enabled, like the bat, to suspend itself
from precipitous rock-walls.
It is a remarkable fact, that, whereas the Pterodactyles of the older
Lias beds did not exceed ten or twelve inches in length, the later
forms, found fossil in the Greensand and Wealden beds of the Lower
Cretaceous formation, must have been at least 16½ feet long. That these
reptiles were not the only vertebrated animals capable of hovering in
the air at the time when the huge Ichthyosaurus was lord of the seas, is
proved by a bird about the size of a rook, which was discovered in 1862,
in the lithographic slate of Solenhofen in Bavaria, a stone-bed
belonging to the period of the Upper Oolite. The skeleton of this
valuable specimen, now in the British Museum, is almost entire, with the
exception of the head, and retains even its feathers. Still older fossil
mammalia have been found near Stuttgard, in the uppermost bed of the
Triassic deposits, and in the Lower Oolite of Oxfordshire. These
interesting remains, which carry back the existence of the mammals to a
very remote period, belong to small marsupial, or opossum-like, animals.
The jaws, which are the principal parts preserved, are exceedingly
minute, and remarkable for the number and distribution of their teeth,
which prove them to have been either insectivorous or rodent.
The remains of the Ichthyosauri and Plesiosauri occur chiefly in the
Liassic group, but the more recent Cretaceous (Wealden) formation is
distinguished by the presence of still more enormous land saurians. On
their massive legs and unwieldy feet these monsters stood much higher
than any reptile of our days, and resembled in bulk and stature the
elephants of the present world.
The carnivorous Megalosaurus (for its sharply serrated teeth indicate
this mode of life) appears to have preceded the gigantic Iguanodon,
whose dentition denotes a vegetable food. Like the giant sloths of South
America—the Megatherium and the Mylodon—the Iguanodon was provided with
a long prehensile tongue and fleshy lips to seize the leaves and
branches on which it fed. Professor Owen estimates its probable length
at between fifty and sixty feet, and to judge by the proportions of its
extremities, and particularly of its huge feet, it must have exceeded
the bulk of the elephant eightfold.
During the following Upper Cretaceous epoch flourished the Mosasaurus, a
marine saurian, first discovered in the quarries of St. Peter’s Mount,
near Maestricht,[1] and supposed to have been twenty-four feet in
length. But the supremacy of the reptiles was now drawing to its close,
and in the Tertiary period we at length see the Mammalia assume a
prominent place on the scene of life. The oldest of these tertiary
quadrupeds differ so widely from those of the present day as to form
distinct genera. The Palæotheriums, for instance, of which there are
seventeen species, varying in dimensions from the size of a rhinoceros
to that of a hog, combine in their skeleton many of the characters of
the tapir, the rhinoceros, and the horse, while the Anoplotheriums,
whose size varied from that of a hare to that of a dwarf ass, resembled
in some respects the rhinoceros and the horse, and in others the
hippopotamus, the hog, and the camel.
Footnote 1:
Chapter XXXVIII
In the Miocene epoch many of these more ancient quadrupeds no longer
appear upon the scene, while others still flourish in its upper period
along with still existing genera, and with forms long since extinct,
such as the Dinotherium. This huge animal is particularly remarkable for
its two large and heavy tusks, placed at the extremity of the lower jaw,
and curved downwards like those in the upper jaw of the walrus. It was
formerly supposed to be an herbivorous cretacean, and to have used its
anterior limbs principally in the act of digging for roots. The remains
on which these speculations were founded were the huge jaws and
shoulder-blade discovered at Epplesheim in Hesse Darmstadt; but an
immense pelvis of the animal, measuring six feet in breadth and four and
a quarter feet in height, discovered by Father Sanno Solaro, in the
department of the Haute Garonne, proves that this supposed aquatic
pachyderm was a gigantic marsupial, and that the dependent trunks of the
unwieldy animal, instead of serving the purpose of anchoring it to the
banks of rivers, answered the more homely, but equally important office,
of lifting the young into the maternal pouch. ‘The remarkable history of
the successive discovery of its bones,’ says Professor Haughton, ‘and
the change of views consequent thereupon, should teach geologists
modesty in the expression of their opinion.’ During this period also
flourished in India, along with many other strange forms of life, the
Colossochelys Atlas, a tortoise of the most gigantic proportions,
measuring, probably, nearly twenty feet on the curve of the carapace,
and dwarfing into insignificance the great Indian tortoise of the
present day.
The nearer we approach our own times, the greater becomes the proportion
of still existing genera and species; and it is remarkable that as early
as the Pliocene epoch we find a geographical distribution of mammalian
life analogous to that which now characterises the various regions of
the earth.
Thus the fossil monkeys of South America have the nostrils wide apart
like all the existing simiæ of the new world, and fossil monkeys with
approximated nostrils, the characteristic mark of all the old world
quadrumana, are exclusively found in Asia and in Europe, where now a
small species of monkey is confined to the Rock of Gibraltar, but where,
in the Upper Miocene times, large long-armed apes, equalling man in
stature, lived in the oak forests of France. Thus also South America,
where alone sloths and armadilloes exist at the present day, is the only
part of the world where, in the younger tertiary rocks, the remains of
analogous mammals—the Megatherium, the Mylodon, and the Glyptodon—have
been found.
The Mylodon was a colossal sloth, eleven feet long and with a
corresponding girth. When we consider the huge size of the pelvis and
the massiveness of the limbs, we must needs conclude that Professor Owen
could not possibly have given the unwieldy animal a more appropriate
surname than that of _robustus_.
The Megatherium was of still larger size. Its length was as much as
eighteen feet, the breadth of its pelvis was six feet, and the tail,
where it was attached to the body, must have measured six feet in
circumference. The thigh bone was nearly three times as great as that of
the largest known elephant, the bones of the instep and those of the
foot being also of corresponding size. The general proportions both of
the Megatherium and Mylodon resembled those of the elephant, the body
being relatively as large, the legs shorter and thicker, and the neck
very little longer. The Megatherium may have had a short proboscis, but
the Mylodon exhibits no mark of such contrivance.
It is evident, from the bulk and construction of these huge animals,
that they did not, like the sloths of the present day, crawl along the
under side of the boughs till they had reached a commodious feeding
place, but that, firmly seated on the strong tripod of their two hind
legs and powerful tail, they uprooted trees or wrenched off branches
with their fore limbs, which were well adapted for grasping the trunk or
larger branches of a tree. The long and powerful claws were also, no
doubt, useful in the preliminary process of scratching away the soil
from the roots of the trees to be prostrated. This task accomplished,
the long and curved fore claws would next be applied to the opposite
sides of the loosened trunk. ‘The tree being thus partly undermined and
firmly grappled with, the muscles of the trunk, the pelvis, and hind
limbs, animated by the nervous influence of the unusually large spinal
cord, would combine their forces with those of the anterior members in
the efforts at prostration. If now we picture to ourselves the massive
frame of the Megatherium, convulsed with the mighty wrestling, every
vibrating fibre reacting upon its bony attachment with a force which the
sharp and strong crests and apophyses loudly bespeak, we may suppose
that that tree must have been strong indeed which, rocked to and fro, to
right and left, in such an embrace, could long withstand the efforts of
its ponderous assailant.’
[Illustration: GLYPTODON CLAVIPES.]
The Glyptodon, a colossal armadillo of the size of an ox, was covered
with a thick heavy tessellated bony armour, which, when detached from
the body, resembled the section of a large cask. This harness measured
on its curve from head to tail at least six feet, and four feet from
side to side, so that a Laplander might have squatted comfortably under
its roof.
In the superficial deposits of diluvial drift, in Germany and England,
in Italy and Spain, in Northern Asia as well as in North America,
between the latitudes of 40° and 75°, the bones of the large extinct
Pachyderms have been found, and become more and more abundant as we
approach the ice-bound regions within the Arctic Circle. The Siberian
tundras, and the islands in the Polar Sea beyond, are, above all, so
rich in the fossil remains of the Mammoth, or primitive elephant, that
its tusks form a not unimportant branch of commerce. From the presence
of so large an animal in treeless wilds, where now only small rodents or
their persecutors, the Arctic fox and snow owl, find the means of
subsistence, it has been inferred that Siberia must in those times have
enjoyed a tropical climate; but many weighty arguments have been arrayed
against this opinion. The musk-ox, it is well known, prefers the stinted
herbage of the Arctic regions, while the allied buffalo can only thrive
in a warm country, and different species of bears are found in all
zones; so also the primitive elephant was formed for a temperate or cold
climate. Instead of being naked, like his living Asiatic and African
relations, the Mammoth was covered with a warm clothing, well fitted to
brave a low temperature, a fact sufficiently proved by the carcass of
one of these animals which was found, in the year 1803, imbedded in a
mass of ice on the bank of the Lena in latitude 70°. Its skin was
covered first with black bristles, thicker than horse-hair, from twelve
to sixteen inches in length, secondly with hair of a reddish-brown
colour, about four inches long, and thirdly with wool of the same colour
as the hair, about an inch in length.
The discoveries of Middendorff on the banks of the Taymur likewise show
that in those times the climate of Siberia was by no means tropical, for
in latitude 75° 15′ he found the trunk of a larch imbedded with the
bones of a Mammoth in an alluvial stratum fifteen feet above the level
of the sea. Fragments of pine leaves have likewise been extracted from
cavities in the molar teeth of a fossil rhinoceros, discovered on the
banks of the Wiljui, in latitude 64°. The numerous land and freshwater
shells accompanying the Mammoth in the highest latitudes are also,
almost without exception, identical with those now existing in Siberia.
The Mastodon, though not uncommon among the fossils of the old world, is
more abundantly found in North America. The molar teeth of this huge
animal, whose grinding surfaces had their crowns studded with conical
eminences, more or less resembling the teats of a cow, differed greatly
from the flat-crowned grinders of the Mammoth; but both had twenty ribs
like the living elephant, and must have been similar in size and general
appearance. The body of the Mastodon would seem to have been longer, its
limbs thicker and shorter, and, perhaps, its form, on the whole, rather
approaching that of the hippopotamus, which it probably resembled also
in some of its habits. Its mouth was broader than that of the elephant,
and although it was certainly provided with a long trunk, it must have
lived on soft succulent food, and it seems to have rarely left the
marshes and muddy ponds, in which it would find ample food.
The most complete, and probably the largest, specimen of the Mastodon
ever found was exhumed in 1845, in the town of Newbury, New York, the
length of the skeleton being twenty-five feet, and its height twelve
feet. From another specimen, found in the same year, in Warren County,
New Jersey, the clay in the interior within the ribs, just where the
contents of the stomach might naturally have been looked for, furnished
some bushels of vegetable substance. A microscopic examination proved
this matter to consist of pieces of small twigs of a coniferous tree of
the cypress family, probably the young shoots of the white cedar (_Thuja
occidentalis_) which is still a native of North America.
This interesting discovery likewise proves that the climate of North
America was then, like that of Siberia, not very different from that of
the present day.
The most remarkable of the fossil Ruminants are found among the deer
tribe. The largest of these is the _Sivatherium giganteum_, discovered
in the Tertiary beds of the sub-Himalayan hills. It was a deer with four
horns, and, to judge by the size of its bones, must have exceeded the
elephant in its dimensions. Near this huge ‘antlered monarch of the
waste’ the extinct _Cervus megaceros_, found in the bogs and shallow
marls of Ireland, appears as a mere dwarf, in spite of its large
branching palmate horns, often weighing eighty pounds, and a
corresponding stature far exceeding that of our modern deer.
The colossal size of many of the extinct plants and animals might seem
to favour the belief that organic life has degenerated from its former
powers; but a survey of existing creation soon proves the vital
principle to be as strong and flourishing as ever.
No fossil tree has yet been found to equal the towering height of the
huge Sequoias and Wellingtonias of California; and though the Horsetails
and Clubmosses of the Carboniferous ages may well be called colossal
when compared with their diminutive representatives of the present day,
yet their height by no means exceeded that of the tall bamboo of India.
No fossil bivalve is as large as the Tridacna of the tropical seas; and
though our nautilus is a mere pigmy when compared with many of the
Ammonites, our naked cuttlefishes are probably as bulky as those of any
of the former geological formations. The living crustaceans and fishes
are not inferior to their predecessors in size, and though the giant
saurians of the past were much larger than our crocodiles, yet they do
not completely dwarf them by comparison. The extinct Dinornis[2] far
surpassed the ostrich in size, but the Mammoth and the Mastodon find
their equal in our elephant; and though the sloths of the present day
are mere pigmies when compared with the Megatherium, yet no extinct
mammal attains the size of the Greenland whale.
Footnote 2:
Chapter XIX.
The perfect preservation of so many fossil remains of animals and
plants, which enables us to trace the progress of organic life on earth
from one vast epoch to another, is surely wonderful enough; but we must
consider it as a still greater wonder that phenomena usually so
evanescent as foot-prints, ripple-marks, and rain-prints should in some
cases have been permanently engraved in stone, and appear as distinct
after millions of years as if their traces had been left but yesterday.
All these marks were at first printed on soft argillaceous mud, on the
sea-shore, or on the borders of lakes and rivers, which retained them as
they became dry. Sand or clay having then been drifted into the mould by
the wind, or deposited in its cavity by the next tide, a permanent cast
was made, indented in the lower stratum and standing out in relief on
the upper one.
Thus rain-drops on greenish slates of the Coal period, with several worm
tracks, such as usually accompany rain-marks on the recent mud of modern
beaches, have been discovered near Sydney, in Cape Breton. As the drops
resemble in their average size those which now fall from the clouds, we
may presume that the atmosphere of the Carboniferous period corresponded
in density with that now investing the globe, and that different
currents of air varied then as now in temperature, so as, by their
mixture, to give rise to the condensation of aqueous vapour.
In like manner it has been possible to detect the footprints of
reptiles, even in shales as old as the Cambrian formation, and to follow
their trail as they walked or crawled along.
In the Upper New Red Sandstone (Lower Trias), near Hildburghausen, in
Saxony, a strange unknown animal, supposed to belong to the frog order,
has left foot-prints bearing a striking resemblance to the impressions
made by a human hand; and in the still older red sandstone of
Connecticut, a gigantic bird has marked a foot four times larger than
that of the ostrich. It existed long before the Ichthyosaurus was seen
on earth, and yet by a singular chance its traces, printed on a
foundation proverbially unstable, have outlived the wreck of so many
ages.
However brief and defective the foregoing review of the fossil world may
have been, it has still sufficed to point out the existence on our
planet of so many habitable surfaces, each distinct in time, and peopled
with its peculiar races of aquatic and terrestrial beings, all admirably
fitted for the new states of the globe as they arose, or they would not
have increased and multiplied and endured for indefinite periods.
‘The proofs now accumulated,’ says Sir Charles Lyell, ‘of the close
analogy between extinct and recent species are such as to leave no doubt
on the mind that the same harmony of parts and beauty of contrivance
which we admire in the living creation has equally characterised the
organic world at remote periods. Thus, as we increase our knowledge of
the inexhaustible variety displayed in living nature, our admiration is
multiplied by the reflection that it is only the last of a great series
of pre-existing creations, of which we cannot estimate the number or
limit in times past.’
CHAPTER III.
SUBTERRANEAN HEAT.
Zone of invariable Temperature—Increasing Temperature of the Earth at a
greater Depth—Proofs found in Mines and Artesian Wells, in Hot Springs
and Volcanic Eruptions—The whole Earth probably at one time a fluid
mass.
Born neither to soar into the air, nor to inhabit the deep waters, nor
to pass his life in subterranean darkness, man is unable to depart to
any considerable distance from the earth’s surface. If he ascends in a
balloon, he soon reaches the limits where the rarefied atmosphere
renders breathing impossible; a few thousand feet limit his efforts to
pierce the earth’s crust; and should he be cast out into the sea, he is
soon drowned. But beyond the limits to which his body is confined, his
mind soars into space, and plunging into the unknown interior of our
globe, seeks to unravel the mystery of its formation. In the following
pages I purpose briefly to point out the circumstances which guide him
in his speculations, and enable him to roam, at least in spirit, through
the profound abysses of the subterranean world.
As we all know, the temperature of the atmosphere soon communicates its
changes to the surface of the earth; and our meadows, which when warmed
by the rays of the sun are green and covered with flowers, harden in
winter into a lifeless plain. But the influence of the sun’s heat upon
the soil is merely superficial, so that in the temperate zones the
annual fluctuations of the thermometer are no longer perceptible at a
depth of from 60 to 80 feet.
Thus, in the cellars of the Parisian observatory, a thermometer, placed
many years ago 86 feet below the surface, invariably indicates +11°7
Celsius; the summer above may be ever so intensely hot, or the winter
ever so cold, the column of mercury never deviates a hair’s breadth from
the height it has once attained. Below these limits the warmth of the
earth gradually increases—a fact placed beyond all doubt by the
innumerable observations that have been made in mines, and during the
boring of Artesian wells. For wherever sinkings have been made, a rising
of the thermometer has always been found to take place as the auger
penetrates to a greater depth below the surface. Thus, to cite but a few
examples, the temperature of the Artesian well of Grenelle in Paris,
which, at a depth of 917 French feet, amounted to +22°2 C., increased at
the depth of 1,555 feet to +26°43, and the water, which now gashes forth
from the depth of 1,684 feet, constantly maintains the same lukewarm
temperature of +27°70.
During the boring of the well of Neusalzwerk, in Westphalia, the
temperature rose at the various depths of 580, 1,285, and 1,935 feet
from +19°7 C. to +27°5 and +31°4, until, finally, when the depth of
2,144 feet was attained, the saline spring issued forth with a constant
temperature of +33°6. As from the experience acquired in mines and
Artesian wells, the temperature is found to increase by one degree for
about every successive 80 or 100 feet, the internal warmth of the earth,
supposing it to increase in the same proportion towards the centre,
would, at the depth of 10,000 feet, be equal to that of boiling water,
and at that of 80 or 100 miles sufficiently great to melt the hardest
rock.
Whether this steady increase really takes place is of course only matter
of conjecture; but the history of hot springs and volcanic eruptions
shows us that everywhere a very high degree of heat exists at
considerable depths below the surface.
Most springs in the temperate zone, without being warm in a remarkable
degree, still possess a higher temperature than the average warmth of
the air in the locality where they gush forth, while in the tropical
zone they are frequently cooler—a proof that in both cases they issue
from a depth independent of the fluctuating atmospherical influences of
the surface. While these cool or cold springs, spread in immense numbers
over the earth, attest the existence everywhere of a subterranean source
of heat, the warm and hot springs remind us of its intensity at more
considerable depths. These thermal sources are confined to no climate,
for in the cold land of the Tschuktschi, where the soil must be
perpetually frozen to a depth of several hundred feet, boiling water is
found to gush forth, as well as in the tropical Feejee Islands.
The hot springs, though of frequent occurrence in all parts of the
world, are not the only or principal vents of subterranean heat. Far
greater quantities of caloric are constantly pouring forth from the
numerous volcanoes and solfataras, which are likewise distributed all
over the surface of the globe. The violent convulsions which attend
every outflow of lava are proofs that these torrents of liquid stone
must have been forced upwards from a far greater depth than the water of
the hot springs. The temperature necessary for their production likewise
points to this fact, for to melt stones a heat of at least 2,000°C. is
required. But volcanoes, like hot springs, are found in every zone;
beyond the Arctic Circle, as well as in the most southern land attained
by Sir James Ross in his memorable voyage. They line the coasts of the
Pacific, as well as those of the Sea of Kamtschatka. They desolate
Iceland, as they devoured Pompeii and Herculaneum; and everywhere they
pour forth the same masses of fluid stone; so that the geologist is not
able to distinguish the lavas of the Andes chain from those of Etna or
Vesuvius. But phenomena so much alike in character, common to all parts
of the globe, can hardly be dependent upon mere local circumstances, and
speak loudly in favour of the theory which supposes our earth to have
been at one time a ball of liquid fire. Wandering through space during a
course of unnumbered ages, this huge mass of molten stones and metals
gradually cooled, and at length got covered with a solid crust, below
which the ancient furnaces are still burning, and striving to burst
their fetters. Well may we say with Horace—
‘_Incedimus_ per ignes
Suppositos cineri doloso.’
CHAPTER IV.
SUBTERRANEAN UPHEAVALS AND DEPRESSIONS.
Oscillations of the Earth’s Surface taking place in the present day—
First ascertained in Sweden—Examples of Contemporaneous Upheaval and
Depression in France and England—Probable Causes of the Phenomenon.
While the sea and the atmospheric ocean are subject to perpetual
fluctuations, and the poet justly compares the uncertain tenure of human
prosperity with the restless wave or the inconstant wind, the solid
earth is generally regarded as the emblem of stability. But an
examination of the various strata of aqueous origin which constitute by
far the greater part of the actual dry land soon shows the fallacy of
this opinion.
The fossils of marine origin which occur in so many of our oldest rocks,
now situated far above the level of the ocean, must necessarily have
been raised from the deep. On the towering Andes, fifteen thousand feet
above the tide-marks of the Pacific, the geologist finds sea-shells
imbedded in the rock, and high above the snow-line the chamois-hunter of
the Alps wonders at the sight of spirally-wound Ammonites that once
enjoyed life at the bottom of the Liassic Sea. In strata of a more
modern date, we find, on the banks of the river Senegal, far inland,
large deposits of the _Arca senilis_, a mollusc still living on the
neighbouring coast. On the borders of Loch Lomond, twenty feet above the
level of the sea, shells of the edible cockle and sea-urchin repose in a
layer of brown clay, and the banks of the Forth and of the Clyde, thirty
feet higher than the storm tides, inclose remains of common shells of
the present period, such as the oyster, the mussel, and the limpet.
Along the shores of the Mediterranean, at Monte Video and at Valparaiso,
in the isles of the Pacific and at the Cape, in California and Haiti, we
meet with similar instances of elevation, which, though geologically
recent, may yet be of a sufficiently ancient date to have preceded the
appearance of man on earth. But proofs are not wanting that the
upheaving power which has wrought so many changes in the past is still
actively employed in remodelling the surface of the earth.
This important geological fact was first ascertained on the coast of
Sweden, where the peculiar configuration of the shore makes it easy to
appreciate slight changes in the relative level of land and water. For
the continent is fringed with countless rocky islands, called the
‘skär,’ within which boats and small vessels sail in smooth water even
when the sea without is strongly agitated. But the navigation is very
intricate, and the pilot must possess a perfect knowledge of the breadth
and depth of every narrow channel, and the position of innumerable
sunken rocks. On such a coast even a slight change of level could not
fail to become known to the mariner, and to attract the attention of the
learned, as soon as the book of nature began to be more accurately
studied.
Early in the last century the Swedish naturalist Celsius collected
numerous observations, all pointing to the fact of a slow elevation of
the land. Rocks both on the shore of the Baltic and the German Ocean,
known to have been once sunken reefs, were in his time above water;
small islands in the Gulf of Bothnia had been joined to the continent,
and old fishing grounds deserted, as being too shallow or entirely dried
up. These changes of level, which he estimated at about three feet in a
century, Celsius attributed to a sinking of the waters of the Baltic,
owing possibly to the channel, by which it discharges its surplus waters
into the Atlantic, having been gradually widened and deepened by the
waves and currents. But the lowering of level would in that case have
been uniform and universal over that inland sea, and the waters could
not have sunk at Torneo while they retained their former level at
Copenhagen, Wismar, Stralsund, and other towns which are now as close to
the water’s edge as at the time of their foundation. Playfair (1802) and
Leopold von Buch (1807) first attributed the change of level to the slow
and insensible rising of the land, and the subsequent investigations of
Sir Charles Lyell in 1834 have placed the fact beyond a doubt.
The attention of geologists having once been directed to the partial
upheaval of the Scandinavian peninsula, similar facts were soon pointed
out in other countries. At Bourgneuf, near La Rochelle, the remains of a
ship wrecked on an oyster bank in the year 1752, now lie in a cultivated
field, fifteen feet above the level of the sea; and, within a period of
twenty-five years the parish has gained at least 1,500 acres, a very
acceptable gift of the subterranean plutonic power. Port Bahaud, where
formerly the Dutchmen used to take in cargoes of salt, is now 9,000 feet
from the sea, and the Island of Olonne is at present surrounded only by
swamps and meadows. These and similar phenomena, such as the constant
rise of the chalk cliffs at Marennes, cannot possibly be explained by
recent driftings, but evidently proceed from a slow upheaval of the
coasts and the adjacent sea-bed.
On the opposite shores of the Atlantic, we find Newfoundland undergoing
a similar process of elevation; for cliffs over which, thirty or forty
years ago, schooners used to sail with perfect safety, are now quite
close to the surface; and in the Pacific the depth of the channel
leading to the port of Honolulu is gradually decreasing from the same
cause.
While many coasts thus show signs of progressive elevation, others
afford no less striking proofs of subsidence, frequently in close
proximity to regions of upheaval.
Thus on the south-west coast of England, in Cornwall, Devon, and
Somerset, submarine forests, consisting of the species still flourishing
in the neighbourhood, are of such frequent occurrence that, according to
Sir Henry de la Beche, ‘it is difficult not to find traces of them at
the mouths of all the numerous valleys which open upon the sea.’
Sometimes they are covered with mud or sand, and generally the roots are
found in the situation where they originally grew, while the trunks have
been horizontally levelled. At Bann Bridge, specimens of ancient Roman
pottery have been discovered twelve feet below the level of the sea, and
the remains of an old Roman road, now submerged six feet deep, prove
that the subsidence of the land has been going on since the times of
Julius Cæsar and Agricola.
On the east coast the phenomenon is still more striking, particularly in
the Wash, that shallow bay between Lincolnshire and Norfolk on whose
opposite shores a submarine forest extends, the trunks and stubbles of
which become apparent at ebb-tide. On the coasts of Normandy and
Brittany we likewise find traces of depression, pointing to some future
time when perhaps many a bluff headland, now boldly fronting the ocean,
may have disappeared beneath the waves.
Huts of the Esquimaux and of the early Danish colonists on the coast of
Greenland, now submerged at high tide, could not possibly have been
originally constructed in so inconvenient a situation; and at Puynipet,
in the South Sea, habitations sunk beneath the water likewise prove a
gradual subsidence of the land.
On many coasts and islands modern scientific explorers have hewn marks
in the rock, to enable future generations to judge of the changes which
are slowly but surely altering the configuration of the land and tracing
new boundaries to the ocean. Had our forefathers left us similar
memorials, we should know much more about the oscillatory movements of
the earth-rind than we know now; but, unfortunately, experimental
natural philosophy is but of recent date, and the marks chiselled out
upon the Swedish rocks in the years 1731 and 1752 are the earliest
records by which the chronological progress of elevation or subsidence
can be distinctly ascertained.
This phenomenon, which has played so important a part in the physical
annals of our globe, having once been accurately determined, enables the
geologist to explain many facts for which, before it became known, it
was impossible to account.
We now need not wonder at seeing sea-shells imbedded in the highest
mountains or buried hundreds of fathoms under the ground, at alternating
layers of marine and sweet-water deposits being frequently storied one
above the other, or at originally horizontal strata being now found at
every possible angle of inclination.
The imperceptible slowness with which many of these vast changes are
actually taking place warrants the inference that violent volcanic
revolutions have no doubt been far less instrumental in moulding the
earth-rind to its present form than the slow oscillatory movements of
elevation and depression which from time immemorial have been constantly
altering its surface.
The causes of these oscillatory movements are still very imperfectly
known, though a probable hypothesis attributes them to the expansion by
increased temperature of extensive deep-seated masses of matter. As the
elevation of some tracts seems to coincide with the proportionate
depression of others at a greater or less distance, these alternating
upheavals and subsidences may possibly be the result rather of the
lateral shifting of the flow of heat from one mass of subterranean
matter to a neighbouring mass than of its positive increase on the
whole. ‘Such a lateral diversion of the outward flow of heat,’ says Mr.
Poulett Scrope, ‘we may presume to be caused by the deposition over
certain areas of thick newly-formed beds of any matter imperfectly
conducting heat, like sedimentary sands, gravels, clays, shales, or
calcareous mud, by which the outward transmission of heat being checked,
it must accumulate beneath, while a portion of it will pass off
laterally to augment the temperature of mineral matter in neighbouring
areas; just as the water of a spring, if its usual issue is blocked up,
will accumulate in the fissures or pores of the rock containing it,
until it finds a vent on either side and at a higher level. Owing to
this increase, the resistance opposed by the overlying rocks in that
quarter may be sooner or later overcome, and their elevation brought
about, through the dilatation of the mineral matter beneath.’
CHAPTER V.
SUBTERRANEAN WATERS AND ARTESIAN WELLS.
Subterranean Distribution of the Waters—Admirable Provisions of Nature—
Hydrostatic Laws regulating the Flow of Springs—Thermal Springs—
Intermittent Springs—The Geysir—Bunsen’s Theory—Artesian Wells—Le
Puits de Grenelle—Deep Borings—Various Uses of Artesian Wells—Artesian
Wells in Venice and in the Desert of Sahara.
In every zone the evaporating power of the sun raises from the surface
of the ocean vapours, which hover in the air until, condensed by cold,
they descend in rain upon the earth. Here part of them are soon restored
to the sea by the swollen rivers; another part is once more volatilised;
but by far the larger quantity finds its slow way into the bowels of the
earth, where it serves for the perennial supply of wells and springs.
The distribution of these subterranean waters, and the simple laws which
regulate their circulation, afford us one of the most interesting
glimpses into the physical economy of our globe. We know that the
greater part of the earth’s surface is composed of stratified rocks, or
alternate beds of impermeable clay and porous limestone or sand, which
were originally deposited in horizontal layers, but have since been more
or less displaced and set on edge by upheaving forces. Wherever
permeable beds of limestone or sand crop out on the surface of the land,
the residuary portions of rain-water which are not disposed of by floods
or by evaporation, must necessarily penetrate into the pores and
fissures, and descend lower and lower, until they finally reach an
impermeable stratum which forbids their further progress to a greater
depth.
The granite, gneiss, porphyry, lava, and other unstratified and
crystalline rocks of igneous origin, which cover about a third part of
the habitable globe, are likewise intersected by innumerable fissures
and interstices, which, in a similar manner, collect and transmit rain-
water.
Thus the plutonic or volcanic forces which have gradually moulded the
dry land into its present form have also provided it with the necessary
filters, drains, reservoirs, and conduits, for the constant
replenishment of springs, brooks, and rivers. As every porous layer is
more or less saturated with moisture, the stratified rocks are
frequently traversed at various depths by distinct sheets of water, or
rather, in most cases, by permanently drenched or waterlogged sheets of
chalk or sand. Thus, in a boring undertaken in search of coal at St.
Nicolas d’Aliermont, near Dieppe, no less than seven very abundant
aquiferous layers or beds of stone were met with from about 75 to 1,000
feet below the surface. In an Artesian boring at Paris, five distinct
sheets of water, each of them capable of ascension, were ascertained;
and similar perforations executed in the United States, and other
countries, have in the same manner traversed successive stages of
aqueous deposits.
Thus there can be no doubt that vast quantities of water are everywhere
accumulated in the porous strata of which a great part of the
superficial earth-rind is composed, the rapidity with which they
circulate varying of course with the amount of hydrostatic pressure to
which they are subjected, and the more or less porous and permeable
nature of the beds through which they percolate. Were the ground we
stand on composed of transparent crystal, and the subterranean water-
courses tinged with some vivid colour, we should then see the upper
earth-crust traversed in every direction by aqueous veins, and
frequently as saturated with water as the internal parts of our body are
with blood. But Nature not only perennially feeds our springs and brooks
from the inexhaustible fountains of the deep; it is also one of her
infinitely wise provisions that the same water which, if placed in casks
or open tanks, becomes putrid, continues fresh so long as it remains in
the cavities and interstices of the terrestrial strata. While filtering
through the earth, it is generally cleansed of all the organic
substances whose decay would inevitably taint its purity, and comes
forth salubrious and refreshing, a source of health and enjoyment to the
whole animal creation.
The extreme limits to which the waters descend into the earth of course
escape our direct observation, as the lowest point to which the
subterranean regions have been probed is less than 2,000 or 2,500 feet
below the level of the sea; but as we know from the formation of many
basins that the strata of which they are composed attain in many cases a
thickness of from 20,000 to 30,000 feet, there can hardly be a doubt
that they are permeated by water to an equal depth.
As steam plays so great a part in volcanic phenomena, the seat or
effective cause of which must needs be sought for at an immense distance
below the surface of the earth, we have another proof of the vast depth
to which the subterranean migrations of water are able to attain.
After this brief glimpse into the reservoirs of the deep, we have to
ascertain the power which raises their liquid contents and forces them
to reappear upon the surface of the earth. If we pour water into a tube,
bent in the form of the letter U, it will rise to an equal level in both
branches. We will now suppose that the left branch of the tube opens at
the top into a vast reservoir, which is able to keep it constantly
filled, and that the right branch is cut off near the bottom, so that
only a small vertical piece remains. The pressure of the water column in
the left branch will in this case force the liquid to gush out of the
orifice of the shortened right branch to the level which it occupied
while the branch was still entire.
These two hydrostatic laws, or rather these two modifications of the
same law, have been frequently put to practical uses, as, for instance,
in the communicating tubes which distribute the waters of an elevated
source or reservoir to the various districts of a town, or in the
subterranean conduits which serve to create fountains, such as those of
Versailles or the Crystal Palace.
When the Romans intended to lead water from one hill to another, they
constructed, at a vast expense, magnificent aqueducts across the
intermediate valley; but the Turks, whom we look upon as ignorant
barbarians, obtain the same result in a much more economical manner, and
in this respect far surpass the ancients, who, had they been better
acquainted with the first principles of hydrostatics, would indeed have
left us fewer specimens of their architectural skill, but would at the
same time have saved themselves a great deal of unnecessary expense.
Down the slope of the hill from which the water is to be conducted, the
Turks lay a tube of brick or metal, which, crossing the valley, moulds
itself to its different inflections, and ultimately ascends the
declivity of the hill on the opposite side, where, in virtue of the law
above cited, the water rises as high as on that from which it descended.
If we suppose the descending branch of the tube to be prolonged only as
far as the level of the valley, with a superficial orifice, then the
liquid will of course gush forth in a vertical column, and form a _jet
d’eau_, or fountain, its height being determined by the elevation of the
sheet of water by which it is fed, and the consequent degree of pressure
which acts upon it. This is the principle on which all artificial
fountains are constructed. The conduit, for instance, which feeds the
grand fountain of the Tuileries receives its water from a reservoir
situated on the heights of Chaillot.
Whatever the form of the tube may be in which the liquid is contained,
the simple hydrostatic law which regulates its level remains unmodified.
Let the tube be circular, elliptic, or square, with a single orifice or
with many—let it be open or choked with pebbles or permeable sand—in
every case the water will invariably rise to the same height, provided
the tube be perfectly water-tight; or else gush forth wherever it finds
an opening below the highest level.
This hydrostatic principle so perfectly illustrates the origin of
springs, that it is almost superfluous to enter into any further details
on the subject.
When we consider that porous or absorbent strata, alternating with
impermeable strata, frequently crop out on the back or on the slope of
hills or mountains, and then, having reached their base, extend
horizontally beneath the plain, there can be no doubt that they are
placed in the same hydrostatic conditions as ordinary water-conducting
tubes, and that wherever any fissure or opening occurs in the
superincumbent impervious strata at any point below the highest level of
the water, springs must necessarily be formed.
As the same strata often extend over many hundreds of miles, we cannot
wonder that sources frequently issue from the centre of immense plains,
for the hydrostatic pressure which causes them to gush forth may have
its seat at a very considerable distance.
As the waters by which the springs are fed have often vast subterranean
journeys to perform, their temperature is naturally independent of that
of the seasons or of the changes of the atmosphere. Thus, cold springs
occur in a tropical climate, when their subterranean channels descend
from high mountains, and boiling sources gush forth in the Arctic
regions when forced upwards from a considerable depth.
While the waters filter through the earth, they also naturally dissolve
a variety of substances, and hence all springs are more or less
impregnated with extraneous particles. But many of them, particularly
such as are of a higher temperature, contain either a larger quantity or
so peculiar a combination of mineral substances as to acquire medicinal
virtues of the highest order.
The geological phenomena which favour the production of thermal springs
are extremely interesting, and point to a deep-seated origin. By far the
greater number of these fountains arise near the scene of some great
subterranean disturbance, either connected with volcanic action, or with
the elevation of a chain of mountains, or lastly by cliffs and fissures
caused by disruption. Thus the thermal springs of Matlock and Bath
accompany great natural fissures in the mountain limestone, and the hot
springs of Wiesbaden and Ems, of Carlsbad and Toeplitz, all lie
contiguous to remarkable dislocations, or to great lines of elevation,
or to the neighbourhood of a volcanic focus.
One of the most remarkable phenomena of thermal springs is the constant
invariableness of their temperature and their mineral impregnation.
During the last fifty or sixty years, ever since accurate thermometrical
observations and chemical analyses have been made, the most celebrated
mineral sources of Germany have been found to contain the same
proportion of mineral substances. This is truly astonishing when we
consider that the latter are merely dissolved by the waters while
passing through the bowels of the earth, and that a considerable number
of them are frequently found together in the same source.
Another remarkable fact is, that, even in countries exposed to violent
and frequent earthquakes, so many subterranean watercourses have
remained unaltered for 2,000 years at least. The sources of Greece still
flow apparently as in the times of Hellenic antiquity. The spring of
Erasinos, two leagues south of Argos, on the declivity of the Chaonian
mountains, is mentioned by Herodotus. At Delphi the Cassotis (now Wells
of Saint Nicholas) still flow under the ruins of the temple of Apollo,
and the hot baths of Aidepsos still exist in which Sylla bathed during
the Mithridatic war.
Many springs exhibit the singular phenomenon of an intermittence which
is independent of the quantity of rain falling in the district, or of
the flux and reflux of the tide in a neighbouring river. In many cases
the simple and well-known hydrostatical law exemplified in the common
siphon[3] affords a very ready and sufficient explanation of the
phenomenon.
Footnote 3:
A siphon, as is well known, is a bent tube, having one leg longer than
the other. When this tube is filled with any liquid, and the shorter
end is immersed in a vessel containing liquid of the same kind, the
weight of the column in the longer leg will cause the liquid to begin
to run out, and it will continue running till the vessel is emptied.
This arises from the pressure of air on the exposed surface of fluid,
forcing it up through the tube to prevent vacuum, which would
otherwise be formed at the highest point; and the extreme limit of
length at which the siphon will act is therefore determined by the
height of a column of the fluid equal to the pressure of the
atmosphere (fifteen pounds on the square inch). The limit in the case
of water is something more than thirty feet.
[Illustration: siphon]
In the annexed diagram the vessel _a_ communicates, by a tube _c_, with
the siphon tube _b_, and it is manifest that when the water in a rises
above the level of the top of _b_, it will begin to flow over and
escape, as at _d_. But as soon as this is the case the tube _b_ begins
to act as a siphon, and draws off all the water in _a_, so that if a
constant supply is poured into _a_, but at a rate slower than the rate
of the discharge at _d_, there will be an intermittent discharge, the
interval depending on the relation of the rate of filling to that of
emptying.
[Illustration: SECTION OF AN INTERMITTENT SPRING.]
The case of a subterranean cavity in a limestone rock, slowly fed by
drainage from the cracks and fissures of the rock above, and
communicating at a distant point with the surface by a bent or siphon
tube, is evidently strictly analogous.
[Illustration: GEYSIRS OF ICELAND.]
Iceland, pre-eminently the land of volcanic wonders, possesses in the
Great Geysir the most remarkable intermittent fountain in the world. ‘At
the foot of the Laugarfjall hill, in a green plain, through which
several rivers meander like threads of silver, and where chains of dark-
coloured mountains, overtopped here and there by distant snow-peaks,
form a grand but melancholy picture, dense volumes of steam indicate
from afar the site of a whole system of thermal springs congregated on a
small piece of ground not exceeding twelve acres in extent. In any other
spot the smallest of these boiling fountains would arrest the
traveller’s attention, but here his whole mind is absorbed by the Great
Geysir. In the course of countless ages, this monarch of springs has
formed out of the silica which it deposits a mound which rises to about
thirty feet above the general surface of the plain, and slopes on all
sides, to the distance of a hundred feet or thereabouts, from the border
of a large circular basin situated in its centre, and measuring about
fifty-six feet in the greatest diameter and fifty-two feet in the
narrowest. In the middle of this basin, forming as it were a gigantic
funnel, there is a pipe or tube, which at its opening in the basin is
eighteen or sixteen feet in diameter, but narrows considerably at a
little distance from the mouth, and then appears to be not more than ten
or twelve feet in diameter. It has been probed to a depth of seventy
feet, but it is more than probable that hidden channels ramify further
into the bowels of the earth. The sides of the tube are smoothly
polished, and so hard that it is not possible to strike off a piece of
it with a hammer. Generally the whole basin is found filled up to the
brim with sea-green water as pure as crystal, and of a temperature of
from 180° to 190°. Astonished at the placid tranquillity of the pool,
the traveller can hardly believe that he is really standing on the brink
of the far-famed Geysir; but suddenly a subterranean thunder is heard,
the ground trembles under his feet, the water in the basin begins to
simmer, and large bubbles of steam rise from the tube and burst on
reaching the surface, throwing up small jets of spray to the height of
several feet. Every instant he expects to witness the grand spectacle
which has chiefly induced him to visit this northern land; but soon the
basin becomes tranquil as before, and the dense vapours produced by the
ebullition are wafted away by the breeze. These smaller eruptions are
regularly repeated every eighty or ninety minutes, but frequently the
traveller is obliged to wait a whole day or even longer before he sees
the whole power of the Geysir. A detonation louder than usual precedes
one of these grand eruptions; the water in the basin is violently
agitated; the tube boils vehemently; and suddenly a magnificent column
of water, clothed in vapour of a dazzling whiteness, shoots up into the
air with immense impetuosity, to the height of eighty or ninety feet,
and, radiating at its apex, showers water and steam in every direction.
A second eruption and a third rapidly follow, and after a few minutes
the fairy spectacle has passed away like a fantastic vision. The basin
is now completely dried up, and on looking down into the shaft, the
traveller is astonished to see the water about six feet from the rim,
and as tranquil as in an ordinary well. After about thirty or forty
minutes it again begins to rise, and after a few hours reaches the brim
of the basin. Soon the subterranean thunder, the shaking of the ground,
the simmering above the tube begin again—a new gigantic explosion takes
place, to be followed by a new period of rest—and thus this wonderful
play of nature goes on, day after day, year after year, and century
after century. The mound of the Geysir bears witness to its immense
antiquity, as its water contains but a minute portion of silica.’[4]
Footnote 4:
‘The Polar World,’ p. 54.
The explanation of these wonderful phenomena has exercised the ingenuity
of many natural philosophers; but Professor Bunsen’s theory seems the
most plausible. Having first ascertained, by experiment, that the water
at the mouth of the tube has a temperature, corresponding to the
pressure of the atmosphere, of about 212° F., he found it much hotter at
a certain depth below; a thermometer, suspended by a string in the pipe,
rising to 266° F., or no less than 48° above the boiling point. By
letting down stones, suspended by strings, to various depths, he next
came to the conclusion that the tube itself is the main seat or focus of
the mechanical power which forces the huge water column upwards. For the
stones which were sunk, to greater distances from the surface were not
cast up again when the next eruption of the Geysir took place, whereas
those nearer the mouth of the tube were ejected to a considerable height
by the ascending water-column. Other experiments also were made, tending
to demonstrate the singular fact that there is often scarcely any motion
below when a violent rush of steam and water is taking place above. It
seems that when a lofty column of water possesses a temperature
increasing with the depth, any slight ebullition, or disturbance of
equilibrium, in the upper portion may first force up water into the
basin, and then cause it to flow over the edge. A lower portion, thus
suddenly relieved of part of its pressure, expands, and is converted
into vapour more rapidly than the first, owing to its greater heat. This
allows the next subjacent stratum, which is much hotter, to rise and
flash into a gaseous form; and this process goes on till the ebullition
has descended from the middle to near the bottom of the funnel.[5]
Footnote 5:
Liebig’s ‘Annalen,’ translated in ‘Reports and Memoirs of the
Cavendish Society,’ London, 1848, p. 351.
In many geological basins, the deep subterranean waters are frequently
inclosed over a surface of many square miles between impermeable beds of
clay or hard rock, which nowhere permit them to escape; but if a hole be
bored deep enough to reach a permeable bed, it is evident that they will
then gush forth more or less violently, according to the degree of
hydrostatic pressure which acts upon them. This is the simple theory of
the Artesian Wells, so called from the French province of Artois, where,
as far back as the beginning of the twelfth century, springs of water
were artificially obtained by perforating the soil to a certain depth in
places where no indication of springs existed at the surface. The
barbarous inhabitants of the Sahara seem, however, to have long preceded
the Artesians in the art of sinking deep wells, for Olympiodorus, a
writer who flourished at Alexandria about the middle of the sixth
century, mentions pits sunk in the oasis to the depth of 200 or 300
yards, and pouring forth streams of water, used for irrigation.
By the aid of geological science, and of greater mechanical skill,
Artesian borings[6] are at present frequently undertaken in civilised
countries, wherever the nature of the ground promises success, and the
want of water is sufficiently great to warrant the attempt. Sometimes
the water is reached at a moderate distance from the surface, but not
seldom it has been found necessary to bore to a depth of 200 or 300
fathoms. Often efforts, even on this large scale, have proved vain, and
the work has been abandoned in despair.
Footnote 6:
See Chapter on Mines in general, for a short account of earth-boring
operations.
One of the most remarkable instances on record of a successful sinking
for water is that of the Artesian well of Grenelle, one of the Parisian
suburbs.
[Illustration: POROUS STRATA. ARTESIAN WELL SUNK IN THE LONDON BASIN.]
The work was begun with an auger of about a foot in diameter, and the
borings showed successively the alluvial soil and subsoil, and the
tertiary sands, gravels, clays, lignite, &c., until the chalk was
reached. The work was then carried on regularly through the hard upper
chalk down to the lower chalk with green grains, the dimension of the
auger being reduced at 500 feet to a nine-inch, and at 1,300 feet to a
six-inch aperture. When the calculated depth of 1,500 feet had been
reached, and as yet no result appeared, the Government began to be
disheartened. Still, upon the urgent representations of the celebrated
Arago, the sinking was continued, until at length, at the depth of 1,800
feet, the auger, after a violent shock which made the ground tremble,
suddenly turned without an effort. ‘Either the auger is broken, or we
have gained our end,’ exclaimed the director of the work; and a few
moments after, a large column of water gushed out of the orifice. It
took more than seven years to accomplish this grand work (1833–41),
which was retarded by numberless difficulties and accidents. About half-
a-million gallons of perfectly limpid water of a temperature of 82°
Fahr. are daily supplied by the Puits de Grenelle, and amply repay its
cost (362,432 fr. 65 centimes = 14,500_l._).
The high temperature of Artesian springs, when rising from considerable
depths, has been turned to various practical uses. Thus, near Canstadt,
in Wurtemberg, several mills are kept in work, during the severest cold
of winter, by means of the warm water of Artesian wells which has been
turned into the mill-ponds, and at Heilbronn several proprietors save
the expense of fuel by leading Artesian water in pipes through their
green-houses. In some localities the pure and constantly temperate
Artesian waters are made use of for the cultivation of cress. The
vigorous growth of this salutary herb in the beds of rivulets, where
natural springs gush forth, gave the idea of this application, which is
so profitable that the cress nurseries of Erfurt yield a produce of
12,000_l_. a year. Fish ponds have also been improved by such warm
springs being passed through them.
Among the localities benefited by the boring of Artesian wells, Venice
deserves to be particularly noticed. Formerly the City of the Doges had
no other supply of water but that which was conveyed by boats from the
Brenta, or obtained from the rain collected in cisterns. Hence the joy
of the inhabitants may be imagined, when, in 1846, an Artesian boring in
the Piazza San Paolo began to disgorge its water at the rate of forty
gallons per minute, and when other undertakings of the same kind proved
equally successful.
Wherever a well gushes forth in the Sahara, it brings life into the
wilderness; the date-tree flourishes as far as its fertilising waters
extend, and the wandering Arab changes into a sedentary cultivator of
the soil. Thus the boring of Artesian wells on the desert confines of
South Algeria has been the means of wonderful improvement, and if the
French have too often marked their dominion in Africa by a barbarous
oppression of the Arabs, they, in this respect at least, appear in the
more amiable light of public benefactors.
A boring apparatus was first landed at Philippeville in April 1856, and
conveyed with immense difficulty to the Oasis Wad Rir at Tamerna. The
work was begun in May, and on the 19th of June, a spring, to which the
grateful inhabitants gave the name of the ‘Well of Peace,’ gushed forth.
Soon after another source was tapped at Tamelhat, in the Oasis Temacen,
and received the name of the ‘Well of God’s blessing.’
The beneficent instrument of abundance was now conveyed to the Oasis
Sidi Rasched, fifteen miles beyond Tuggurt. Here the auger had scarcely
reached a depth of 120 feet when a perfect stream gushed forth, which,
according to the praiseworthy Arab custom, received the name of the
‘Well of Thanks.’ The opening of this wonderful source gave rise to many
touching scenes. The Arabs came in throngs to witness the joyful
spectacle: each of them poured some of the water over his head, and the
mothers bathed their children in the gushing flood. An old scheik,
unable to conceal his emotion, fell down upon his knees, and shedding
tears of joy, fervently thanked God for having allowed him to witness
such a day.