OOLITE AND LIAS--_continued_.
Mineral character of Lias--Name of Gryphite limestone--Fossil shells
and fish--Ichthyodorulites--Reptiles of the Lias--Ichthyosaur and
Plesiosaur--Marine Reptile of the Galapagos Islands--Sudden
destruction and burial of fossil animals in Lias--Fluvio-marine beds
in Gloucestershire and insect limestone--Origin of the Oolite and
Lias, and of alternating calcareous and argillaceous
formations--Oolitic coal-field of Virginia, in the United States.
_LIAS._--The English provincial name of Lias has been very generally
adopted for a formation of argillaceous limestone, marl, and clay, which
forms the base of the Oolite, and is classed by many geologists as part of
that group. They pass, indeed, into each other in some places, as near
Bath, a sandy marl called the marlstone of the Lias being interposed, and
partaking of the mineral characters of the upper lias and inferior oolite.
These last-mentioned divisions have also some fossils in common, such as
the _Avicula inaequivalvis_ (fig. 302.). Nevertheless the Lias may be traced
throughout a great part of Europe as a separate and independent group, of
considerable thickness, varying from 500 to 1000 feet, containing many
peculiar fossils, and having a very uniform lithological aspect. Although
usually conformable to the oolite, it is sometimes, as in the Jura,
unconformable. In the environs of Lons-le-Saulnier, for instance, in the
department of Jura, the strata of lias are inclined at an angle of about
45 deg., while the incumbent oolitic marls are horizontal.
[Illustration: Fig. 302. _Avicula inaequivalvis_, Sow.]
The peculiar aspect which is most characteristic of the Lias in England,
France, and Germany, is an alternation of thin beds of blue or grey
limestone with a surface becoming light-brown when weathered, these beds
being separated by dark-coloured narrow argillaceous partings, so that
the quarries of this rock, at a distance, assume a striped and
riband-like appearance.[274-A]
Although the prevailing colour of the limestone of this formation is blue,
yet some beds of the lower lias are of a yellowish white colour, and have
been called white lias. In some parts of France, near the Vosges mountains,
and in Luxembourg, M. E. de Beaumont has shown that the lias containing
_Gryphaea arcuata_, _Plagiostoma giganteum_ (see fig. 303.), and other
characteristic fossils, becomes arenaceous; and around the Hartz, in
Westphalia and Bavaria, the inferior parts of the lias are sandy, and
sometimes afford a building stone.
[Illustration: Fig. 303. _Plagiostoma giganteum._ Lias.]
[Illustration: Fig. 304. _Gryphaea incurva_, Sow. (_G. arcuata_, Lam.)]
[Illustration: Fig. 305. _Nautilus truncatus._ Lias.]
The name of Gryphite limestone has sometimes been applied to the lias, in
consequence of the great number of shells which it contains of a species of
oyster, or _Gryphaea_ (fig. 304., see also fig. 30. p. 29.). Many
cephalopoda, also, such as _Ammonite_, _Belemnite_, and _Nautilus_ (fig.
305.), prove the marine origin of the formation.
[Illustration: Fig. 306. Scales of _Lepidotus gigas_, Agas.
_a._ two of the scales detached.]
The fossil fish resemble generically those of the oolite, belonging all,
according to M. Agassiz, to extinct genera, and differing remarkably from
the ichthyolites of the Cretaceous period. Among them is a species of
_Lepidotus_ (_L. gigas_, Agas.) (fig. 306.), which is found in the lias of
England, France, and Germany.[275-A] This genus was before mentioned (p.
229.) as occurring in the Wealden, and is supposed to have frequented both
rivers and coasts. The teeth of a species of _Acrodus_, also, are very
abundant in the lias (fig. 307.).
[Illustration: Fig. 307. _Acrodus nobilis_, Agas. (tooth); commonly called
fossil leach. Lias, Lyme Regis, and Germany.]
[Illustration: Fig. 308. _Hybodus reticulatus_, Agas. Lias, Lyme Regis.
_a._ Part of fin, commonly called Ichthyodorulite.
_b._ Tooth.]
But the remains of fish which have excited more attention than any others,
are those large bony spines called _ichthyodorulites_ (_a_, fig. 308.),
which were once supposed by some naturalists to be jaws, and by others
weapons, resembling those of the living _Balistes_ and _Silurus_; but which
M. Agassiz has shown to be neither the one nor the other. The spines, in
the genera last mentioned, articulate with the backbone, whereas there are
no signs of any such articulation in the ichthyodorulites. These last
appear to have been bony spines which formed the anterior part of the
dorsal fin, like that of the living genera _Cestracion_ and _Chimaera_ (see
_a_, fig. 309.). In both of these genera, the posterior concave face is
armed with small spines like that of the fossil _Hybodus_ (fig. 308.), one
of the shark family found fossil at Lyme Regis. Such spines are simply
imbedded in the flesh, and attached to strong muscles. "They serve," says
Dr. Buckland, "as in the _Chimaera_ (fig. 309.), to raise and depress the
fin, their action resembling that of a moveable mast, raising and lowering
backwards the sail of a barge."[276-A]
[Illustration: Fig. 309. _Chimaera monstrosa._[276-B]
_a._ Spine forming anterior part of the dorsal fin.]
_Reptiles of the Lias._--It is not, however, the fossil fish which form the
most striking feature in the organic remains of the Lias; but the reptiles,
which are extraordinary for their number, size, and structure. Among the
most singular of these are several species of _Ichthyosaurus_ and
_Plesiosaurus_. The genus _Ichthyosaurus_, or fish-lizard, is not confined
to this formation, but has been found in strata as high as the chalk-marl
and gault of England, and as low as the muschelkalk of Germany, a formation
which immediately succeeds the lias in the descending order.[276-C] It is
evident from their fish-like vertebrae, their paddles, resembling those of a
porpoise or whale, the length of their tail, and other parts of their
structure, that the habits of the Ichthyosaurs were aquatic. Their jaws and
teeth show that they were carnivorous; and the half-digested remains of
fishes and reptiles, found within their skeletons, indicate the precise
nature of their food.[276-D]
A specimen of the hinder fin or paddle of _Ichthyosaurus communis_ was
discovered in 1840 at Barrow-on-Soar, by Sir P. Egerton, which
distinctly exhibits on its posterior margin the remains of cartilaginous
rays that bifurcate as they approach the edge, like those in the fin of
a fish (see _a_, fig. 312.). It had previously been supposed, says Mr.
Owen, that the locomotive organs of the Ichthyosaurus were enveloped,
while living, in a smooth integument, like that of the turtle and
porpoise, which has no other support than is afforded by the bones and
ligaments within; but it now appears that the fin was much larger,
expanding far beyond its osseous framework, and deviating widely in its
fish-like rays from the ordinary reptilian type. In fig. 312. the
posterior bones, or digital ossicles of the paddle, are seen near _b_;
and beyond these is the dark carbonized integument of the terminal half
of the fin, the outline of which is beautifully defined.[277-A] Mr. Owen
believes that, besides the fore-paddles, these short-and stiff-necked
saurians were furnished with a tail-fin without bones and purely
tegumentary, expanding in a vertical direction; an organ of motion which
enabled them to turn their heads rapidly.[277-B]
[Illustration: Fig. 310. _Ichthyosaurus communis_, restored by
Conybeare and Cuvier.
_a._ costal vertebrae.]
[Illustration: Fig. 311. _Plesiosaurus dolichodeirus_, restored by
Rev. W. D. Conybeare.
_a._ cervical vertebra.]
[Illustration: Fig. 312. Posterior part of hind fin or paddle of
_Ichthyosaurus communis_.]
Mr. Conybeare was enabled, in 1824, after examining many skeletons nearly
perfect, to give an ideal restoration of the osteology of this genus, and
of that of the _Plesiosaurus_.[278-A] (See figs. 310, 311.) The latter
animal had an extremely long neck and small head, with teeth like those of
the crocodile, and paddles analogous to those of the _Ichthyosaurus_, but
larger. It is supposed to have lived in shallow seas and estuaries, and to
have breathed air like the Ichthyosaur, and our modern cetacea.[278-B] Some
of the reptiles above mentioned were of formidable dimensions. One specimen
of _Ichthyosaurus platyodon_, from the lias at Lyme, now in the British
Museum, must have belonged to an animal more than 24 feet in length; and
another of the _Plesiosaurus_, in the same collection, is 11 feet long. The
form of the _Ichthyosaurus_ may have fitted it to cut through the waves
like the porpoise; but it is supposed that the _Plesiosaurus_, at least the
long-necked species (fig. 311.), was better suited to fish in shallow
creeks and bays defended from heavy breakers.
In many specimens both of Ichthyosaur and Plesiosaur the bones of the head,
neck, and tail, are in their natural position, while those of the rest of
the skeleton are detached and in confusion. Mr. Stutchburg has suggested
that their bodies after death became inflated with gases, and, while the
abdominal viscera were decomposing, the bones, though disunited, were
retained within the tough dermal covering as in a bag, until the whole,
becoming water-logged, sank to the bottom.[278-C] As they belonged to
individuals of all ages they are supposed, by Dr. Buckland, to have
experienced a violent death; and the same conclusion might also be drawn
from their having escaped the attacks of their own predaceous race, or of
fishes, found fossil in the same beds.
[Illustration: Fig 313. _Amblyrhynchus cristatus_, Bell. Length varying
from 3 to 4 feet. The only existing marine lizard now known.
_a._ Tooth, natural size and magnified.]
For the last twenty years, anatomists have agreed that these extinct
saurians must have inhabited the sea; and it was argued that, as there
are now chelonians, like the tortoise, living in fresh water, and
others, as the turtle, frequenting the ocean, so there may have been
formerly some saurians proper to salt, others to fresh water. The common
crocodile of the Ganges is well known to frequent equally that river and
the brackish and salt water near its mouth; and crocodiles are said in
like manner to be abundant both in the rivers of the Isla de Pinos (or
Isle of Pines), south of Cuba, and in the open sea round the coast. More
recently a saurian has been discovered of aquatic habits and exclusively
marine. This creature was found in the Galapagos Islands, during the
visit of H. M. S. Beagle to that archipelago, in 1835, and its habits
were then observed by Mr. Darwin. The islands alluded to are situated
under the equator, nearly 600 miles to the westward of the coast of
South America. They are volcanic, some of them being 3000 or 4000 feet
high; and one of them, Albemarle Island, 75 miles long. The climate is
mild; very little rain falls; and, in the whole archipelago, there is
only one rill of fresh water that reaches the coast. The soil is for the
most part dry and harsh, and the vegetation scanty. The birds, reptiles,
plants, and insects are, with very few exceptions, of species found no
where else in the world, although all partake, in their general form, of
a South American type. Of the mammalia, says Mr. Darwin, one species
alone appears to be indigenous, namely, a large and peculiar kind of
mouse; but the number of lizards, tortoises, and snakes is so great,
that it may be called a land of reptiles. The variety, indeed, of
species is small; but the individuals of each are in wonderful
abundance. There is a turtle, a large tortoise (_Testudo Indicus_), four
lizards, and about the same number of snakes, but no frogs or toads. Two
of the lizards belong to the family _Iguanidae_ of Bell, and to a
peculiar genus (_Amblyrhynchus_) established by that naturalist, and so
named from their obtusely truncated head and short snout.[279-A] Of
these lizards one is terrestrial in its habits, and burrows in the
ground, swarming everywhere on the land, having a round tail, and a
mouth somewhat resembling in form that of the tortoise. The other is
aquatic, and has its tail flattened laterally for swimming (see fig.
313.). "This marine saurian," says Mr. Darwin, "is extremely common on
all the islands throughout the archipelago. It lives exclusively on the
rocky sea-beaches, and I never saw one even ten yards inshore. The usual
length is about a yard, but there are some even 4 feet long. It is of a
dirty black colour, sluggish in its movements on the land; but, when in
the water, it swims with perfect ease and quickness by a serpentine
movement of its body and flattened tail, the legs during this time being
motionless, and closely collapsed on its sides. Their limbs and strong
claws are admirably adapted for crawling over the rugged and fissured
masses of lava which everywhere form the coast. In such situations, a
group of six or seven of these hideous reptiles may oftentimes be seen
on the black rocks, a few feet above the surf, basking in the sun with
outstretched legs. Their stomachs, on being opened, were found to be
largely distended with minced sea-weed, of a kind which grows at the
bottom of the sea at some little distance from the coast. To obtain
this, the lizards go out to sea in shoals. One of these animals was sunk
in salt water, from the ship, with a heavy weight attached to it, and
on being drawn up again after an hour it was quite active and unharmed.
It is not yet known by the inhabitants where this animal lays its eggs;
a singular fact, considering its abundance, and that the natives are
well acquainted with the eggs of the terrestrial _Amblyrhynchus_,
which is also herbivorous."[280-A]
In those deposits now forming by the sediment washed away from the
wasting shores of the Galapagos Islands the remains of saurians, both of
the land and sea, as well as of chelonians and fish, may be mingled with
marine shells, without any bones of land quadrupeds or batrachian
reptiles; yet even here we should expect the remains of marine mammalia
to be imbedded in the new strata, for there are seals, besides several
kinds of cetacea, on the Galapagian shores; and, in this respect, the
parallel between the modern fauna, above described, and the ancient one
of the lias, would not hold good.
_Sudden destruction of saurians._--It has been remarked, and truly, that
many of the fish and saurians, found fossil in the lias, must have met with
sudden death and immediate burial; and that the destructive operation,
whatever may have been its nature, was often repeated.
"Sometimes," says Dr. Buckland, "scarcely a single bone or scale has been
removed from the place it occupied during life; which could not have
happened had the uncovered bodies of these saurians been left, even for a
few hours, exposed to putrefaction, and to the attacks of fishes, and other
smaller animals at the bottom of the sea."[280-B] Not only are the
skeletons of the Ichthyosaurs entire, but sometimes the contents of their
stomachs still remain between their ribs, as before remarked, so that we
can discover the particular species of fish on which they lived, and the
form of their excrements. Not unfrequently there are layers of these
coprolites, at different depths in the lias, at a distance from any entire
skeletons of the marine lizards from which they were derived; "as if," says
Sir H. De la Beche, "the muddy bottom of the sea received small sudden
accessions of matter from time to time, covering up the coprolites and
other exuviae which had accumulated during the intervals."[281-A] It is
farther stated that, at Lyme Regis, those surfaces only of the coprolites
which lay uppermost at the bottom of the sea have suffered partial decay,
from the action of water before they were covered and protected by the
muddy sediment that has afterwards permanently enveloped them.[281-B]
Numerous specimens of the pen-and-ink fish (_Sepia loligo_, Lin.; _Loligo
vulgaris_, Lam.) have also been met with in the lias at Lyme, with the
ink-bags still distended, containing the ink in a dried state, chiefly
composed of carbon, and but slightly impregnated with carbonate of lime.
These cephalopoda, therefore, must, like the saurians, have been soon
buried in sediment; for, if long exposed after death, the membrane
containing the ink would have decayed.[281-C]
As we know that river fish are sometimes stifled, even in their own
element, by muddy water during floods, it cannot be doubted that the
periodical discharge of large bodies of turbid fresh water into the sea may
be still more fatal to marine tribes. In the Principles of Geology I have
shown that large quantities of mud and drowned animals have been swept down
into the sea by rivers during earthquakes, as in Java, in 1699; and that
undescribable multitudes of dead fishes have been seen floating on the sea
after a discharge of noxious vapours during similar convulsions.[281-D]
But, in the intervals between such catastrophes, strata may have
accumulated slowly in the sea of the lias, some being formed chiefly of one
description of shell, such as ammonites, others of gryphites.
From the above remarks the reader will infer that the lias is for the most
part a marine deposit. Some members, however, of the series, especially in
the lowest part of it, have an estuary character, and must have been formed
within the influence of rivers. In Gloucestershire, where there is a good
type of the lias of the West of England, it may be divided into an upper
mass of shale with a base of marlstone, and a lower series of shales with
underlying limestones and shales. We learn from the researches of the Rev.
P. B. Brodie[281-E], that in the superior of these two divisions numerous
remains of insects and plants have been detected in several places, mingled
with marine shells; but in the inferior division similar fossils are still
more plentiful. One band, rarely exceeding a foot in thickness, has been
named the "insect limestone." It passes upwards into a shale containing
_Cypris_ and _Estheria_, and is charged with the wing-cases of several
genera of coleoptera, and with some nearly entire beetles, of which the
eyes are preserved. The nervures of the wings of neuropterous insects
(fig. 314.) are beautifully perfect in this bed. Ferns, with leaves of
monocotyledonous plants, and freshwater shells, such as _Cyclas_ and
_Unio_, accompany the insects in some places, while in others marine shells
predominate, the fossils varying apparently as we examine the bed nearer or
farther from the ancient land, or the source whence the fresh water was
derived. There are two, or even three, bands of "insect limestone" in
several sections, and they have been ascertained by Mr. Brodie to retain
the same lithological and zoological characters when traced from the centre
of Warwickshire to the borders of the southern part of Wales. After
studying 300 specimens of these insects from the lias, Mr. Westwood
declares that they comprise both wood-eating and herb-devouring beetles of
the Linnean genera _Elater_, _Carabus_, &c., besides grasshoppers
(_Gryllus_), and detached wings of dragon-flies and may-flies, or insects
referable to the Linnean genera _Libellula_, _Ephemera_, _Hemerobius_, and
_Panorpa_, in all belonging to no less than twenty-four families. The size
of the species is usually small, and such as taken alone would imply a
temperate climate; but many of the associated organic remains of other
classes must lead to a different conclusion.
[Illustration: Fig. 314. Wing of a neuropterous insect, from the Lower
Lias, Gloucestershire. (Rev. B. Brodie.)]
_Fossil plants._--Among the vegetable remains of the Lias, several species
of _Zamia_ have been found at Lyme Regis, and the remains of coniferous
plants at Whitby. Fragments of wood are common, and often converted into
limestone. That some of this wood, though now petrified, was soft when it
first lay at the bottom of the sea, is shown by a specimen now in the
museum of the Geological Society (see fig. 315.), which has the form of an
_ammonite_ indented on its surface.
[Illustration: Fig. 315. Petrified wood.]
M. Ad. Brongniart enumerates forty-seven liassic acrogens, most of them
ferns; and fifty gymnogens, of which thirty-nine are cycads, and eleven
conifers. Among the cycads the predominance of _Zamites_ and _Nilsonia_,
and among the ferns the numerous genera with leaves having reticulated
veins (as in fig. 296. p. 272.), are mentioned as botanical
characteristics of this era.[282-A]
_Origin of the Oolite and Lias._--If we now endeavour to restore, in
imagination, the ancient condition of the European area at the period of
the Oolite and Lias, we must conceive a sea in which the growth of coral
reefs and shelly limestones, after proceeding without interruption for
ages, was liable to be stopped suddenly by the deposition of clayey
sediment. Then, again, the argillaceous matter, devoid of corals, was
deposited for ages, and attained a thickness of hundreds of feet, until
another period arrived when the same space was again occupied by
calcareous sand, or solid rocks of shell and coral, to be again succeeded
by the recurrence of another period of argillaceous deposition. Mr.
Conybeare has remarked of the entire group of Oolite and Lias, that it
consists of repeated alternations of clay, sandstone, and limestone,
following each other in the same order. Thus the clays of the lias are
followed by the sands of the inferior oolite, and these again by shelly and
coralline limestone (Bath oolite, &c.); so, in the middle oolite, the
Oxford clay is followed by calcareous grit and "coral rag;" lastly, in the
upper oolite, the Kimmeridge clay is followed by the Portland sand and
limestone.[283-A] The clay beds, however, as Sir H. De la Beche remarks,
can be followed over larger areas than the sands or sandstones.[283-B] It
should also be remembered that while the oolitic system becomes arenaceous,
and resembles a coal-field in Yorkshire, it assumes, in the Alps, an almost
purely calcareous form, the sands and clays being omitted; and even in the
intervening tracts, it is more complicated and variable than appears in
ordinary descriptions. Nevertheless, some of the clays and intervening
limestones do, in reality, retain a pretty uniform character, for distances
of from 400 to 600 miles from east to west and north to south.
According to M. Thirria, the entire oolitic group in the department of the
Haute-Saone, in France, may be equal in thickness to that of England; but
the importance of the argillaceous divisions is in the inverse ratio to
that which they exhibit in England, where they are about equal to twice the
thickness of the limestones, whereas, in the part of France alluded to,
they reach only about a third of that thickness.[283-C] In the Jura the
clays are still thinner; and in the Alps they thin out and almost vanish.
In order to account for such a succession of events, we may imagine,
first, the bed of the ocean to be the receptacle for ages of fine
argillaceous sediment, brought by oceanic currents, which may have
communicated with rivers, or with part of the sea near a wasting coast.
This mud ceases, at length, to be conveyed to the same region, either
because the land which had previously suffered denudation is depressed
and submerged, or because the current is deflected in another direction
by the altered shape of the bed of the ocean and neighbouring dry land.
By such changes the water becomes once more clear and fit for the growth
of stony zoophytes. Calcareous sand is then formed from comminuted shell
and coral, or, in some cases, arenaceous matter replaces the clay;
because it commonly happens that the finer sediment, being first drifted
farthest from coasts, is subsequently overspread by coarse sand, after
the sea has grown shallower, or when the land, increasing in extent,
whether by upheaval or by sediment filling up parts of the sea, has
approached nearer to the spots first occupied by fine mud.
In order to account for another great formation, like the Oxford clay,
again covering one of coral limestone, we must suppose a sinking down
like that which is now taking place in some existing regions of coral
between Australia and South America. The occurrence of subsidences, on
so vast a scale, may have caused the bed of the ocean and the adjoining
land, throughout great parts of the European area, to assume a shape
favourable to the deposition of another set of clayey strata; and this
change may have been succeeded by a series of events analogous to that
already explained, and these again by a third series in similar order.
Both the ascending and descending movements may have been extremely
slow, like those now going on in the Pacific; and the growth of every
stratum of coral, a few feet of thickness, may have required centuries
for its completion, during which certain species of organic beings
disappeared from the earth, and others were introduced in their place;
so that, in each set of strata, from the Upper Oolite to the Lias, some
peculiar and characteristic fossils were embedded.
_Oolite and Lias of the United States._
[Illustration: Fig. 316. Section showing the geological position of the
James River, or East Virginian Coal-field.
A. Granite, gneiss, &c.
B. Coal-measures.
C. Tertiary strata.
D. Drift or _ancient alluvium_.]
There are large tracts on the globe, as in Russia and the United States,
where all the members of the oolitic series are unrepresented. In the state
of Virginia, however, at the distance of about 13 miles eastward of
Richmond, the capital of that State, there is a regular coal-field
occurring in a depression of the granite rocks (see section, fig. 316.),
which Professor W. B. Rogers first correctly referred to the age of the
lower part of the Jurassic group. This opinion I was enabled to confirm
after collecting a large number of fossil plants, fish, and shells, and
examining the coal-field throughout its whole area. It extends 26 miles
from north to south, and from 4 to 12, from east to west. The plants
consist chiefly of zamites, calamites, and equisetums, and these last are
very commonly met with in a vertical position more or less compressed
perpendicularly. It is clear that they grew in the places where they now
lie buried in strata of hardened sand and mud. I found them maintaining
their erect attitude, at points many miles distant from others, in beds
both above and between the seams of coal. In order to explain this fact we
must suppose such shales and sandstones to have been gradually accumulated
during the slow and repeated subsidence of the whole region.
It is worthy of remark that the _Equisetum columnare_ of these Virginian
rocks appears to be undistinguishable from the species found in the
oolitic sandstones near Whitby in Yorkshire, where it also is met with
in an upright position. One of the American ferns, _Pecopteris
Whitbyensis_, is also a species common to the Yorkshire oolites.[285-A]
These Virginian coal-measures are composed of grits, sandstones, and
shales, exactly resembling those of older or primary date in America and
Europe, and they rival or even surpass the latter in the richness and
thickness of the seams. One of these, the main seam, is in some places
from 30 to 40 feet thick, composed of pure bituminous coal. On
descending a shaft 800 feet deep, in the Blackheath mines in
Chesterfield county, I found myself in a chamber more than 40 feet high,
caused by the removal of this coal. Timber props of great strength
supported the roof, but they were seen to bend under the incumbent
weight. The coal is like the finest kinds shipped at Newcastle, and when
analysed yields the same proportions of carbon and hydrogen, a fact
worthy of notice when we consider that this fuel has been derived from
an assemblage of plants very distinct specifically, and in part
generically, from those which have contributed to the formation of
the ancient or paleozoic coal.
The fossil fish of these Richmond strata belong to the liassic genus
_Tetragonolepis_, and to a new genus which I have called _Dictyopyge_.
Shells are very rare, as usually in all coal-bearing deposits, but a
species of _Posidonomya_ is in such profusion in some shaley beds as to
divide them like the plates of mica in micaceous shales (see fig. 317.).
[Illustration: Fig. 317. Oolitic coal-shale, Richmond, Virginia.
_a._ _Posidonomya._
_b._ young of same.]
In India, especially in Cutch, a formation occurs clearly referable to the
oolitic and liassic type, as shown by the shells, corals, and plants; and
there also coal has been procured from one member of the group.
FOOTNOTES:
[274-A] Conyb. and Phil. p. 261.
[275-A] Agassiz, Pois. Fos. vol. ii. tab. 28, 29.
[276-A] Bridgewater Treatise, p. 290.
[276-B] Agassiz, Poissons Fossiles, vol. iii. tab. C. fig. 1.
[276-C] Ibid. p. 168.
[276-D] Ibid. p. 187.
[277-A] Geol. Soc. Proceedings, vol. iii. p. 157. 1839.
[277-B] Geol. Trans. Second Series, vol. v. p. 511.
[278-A] Geol. Trans., Second Series, vol. i. pl. 49.
[278-B] Conybeare and De la Beche. Geol. Trans.; and Buckland,
Bridgew. Treat., p. 203.
[278-C] Quart. Geol. Journ. vol. ii. p. 411.
[279-A] +Amblys+, _amblys_, blunt; and +rhygchos+, _rhynchus_, snout.
[280-A] Darwin's Journal, chap. xix.
[280-B] Bridgew. Treat., p. 125.
[281-A] Geological Researches, p. 334.
[281-B] Buckland, Bridgew. Treat., p. 307.
[281-C] Ibid.
[281-D] See Principles, _Index_, Lancerote, Graham Island, Calabria.
[281-E] A History of Fossil Insects, &c. 1845. London.
[282-A] Tableau des Veg. Fos. 1849, p. 105.
[283-A] Con. and Phil., p. 166.
[283-B] Geol. Researches, p. 337.
[283-C] Burat's D'Aubuisson, tom. ii. p. 456.
[285-A] See description of the coal-field by the author, and the plants by
C. J. F. Bunbury, Esq., Quart. Geol. Journ., vol. iii. p. 281.