anastomosing.[102]
16. Poacites.--Leaves linear; ribs parallel.
17. Palmacites.--Leaves fan-shape.
[Footnote 100: M. Brongniart considers these to belong to some
extinct genus of plants, allied to, although perfectly distinct from,
the recent genus _Marsilea_.]
[Footnote 101: These the author thinks are the remains of an extinct
genus of plants.]
[Footnote 102: The character of the ribs here given belongs
exclusively to leaves of plants of the dicotyledonous tribe; as those
of the next genus _Poacites_ equally restricts them to the other
great tribe of monocotyledonous plants.]
Class IV. _Organs of fructification._
Order I. Carpolithes.--Fruits or seeds.
Order II. Antholithes.--Flowers.[103]
[Footnote 103: These orders are too little known to be divided at
present into genera.]
The numerous additions and modifications, which subsequent experience
and discoveries have led M. Brongniart to introduce into his
classification, will be found in an article recently published (1849)
in the "Dictionnaire Universel d'Histoire Naturelle," under the title
of "Tableau des Genres de Végétaux Fossiles, considérés sous le point
de vue de leur classification botanique et de leur distribution
géologique."
V. Fossil Cephalopoda, Nautilus, Ammonite, &c.--The fossil remains
of the molluscous animals, named _Cephalopoda_, from their organs
of prehension being arranged around the head or upper part of the
body, are the most ancient, numerous, and interesting, of this class
of animated nature in the mineral kingdom. These relics are among
the most varied and striking of the extinct beings that occur in
the sedimentary strata, from the most ancient secondary formations,
to the most recent tertiary. The living species are but a feeble
representation of the countless myriads which must have swarmed in
the ancient seas.
The animal of the Cephalopods is composed of a body, which is either
enclosed in a shell, as in the Nautilus, or contains a calcareous
osselet or support, as in the Sepia or Cuttle-fish; it has a distinct
head, and eyes as perfect as in the vertebrated animals, with
complicated organs of hearing, and a powerful masticating apparatus,
surrounded by arms or tentacula. Below the head there is a tube which
acts as a locomotive instrument, to propel the animal backwards, by
the forcible ejection of the water that has served the purpose of
respiration, and which can be ejected with considerable force by the
contraction of the body.
Their fossil remains consist of the external shell and the internal
osselet; and in the naked tribes, of the soft parts of the body,
the ink-bag, &c., as noticed in the account of the Belemnite and
Belemnoteuthis.
The shell varies exceedingly in the different genera. In the group
characterised by smooth septa, and a medial or submedial siphuncle,
as the Nautilus, the earliest or most ancient type is straight, as in
the _Orthoceras_ (Plate LVIII. fig. 14) of the palæozoic formations;
the intermediate forms present various modifications of the spiral,
and terminate in the completely discoidal shell of the living genus;
while the other group, that with sinuous or foliated septa and a
dorsal siphuncle, commences in a discoidal type--the Ammonite, which
gradually passes through the various modifications of _Crioceras_,
_Scaphites_ (Plate LXI. fig. 10), _Hamites_ (Plate LXI. fig. 3),
_Turrilites_ (Plate LXI. fig. 12), &c.; and finally becomes extinct
in the straight Baculites (Plate LX. fig. 2).
In argillaceous strata, as the Kimmeridge and Oxford clay, London
clay, &c., the shells of Cephalopoda are oftentimes beautifully
preserved; the chambers are frequently filled with the solid matrix,
but in many instances these cavities are lined either with brilliant
pyrites or spar. Stony or sparry casts of the cells or chambers, the
shell having perished, are another common state in which vestiges of
these animals occur. Sometimes the cast of each chamber is isolated,
so as to present a series from the innermost to the outermost
cell. Sections of those casts, in which the chambers are filled up
with spar, constitute specimens of great beauty and interest. The
so-called snake-stones are, of course, mere casts of Ammonites;[104]
those of Whitby, from the lias limestone, are well known to every
collector; the casts of a very large species are common in the
oolite, especially at Swindon, in Wiltshire, and in the neighbourhood
of Bath.
VI. The Carboniferous Deposits, or Coal Measures.--The various
deposits of Coal have manifestly been formed under different local
circumstances. Some have been peat-bogs, to which repeated additions
have been made by successive subsidences of the land; others have
been deposited at the bottom of lakes and rivers, and these are
associated with remains of fresh-water shells and Crustacea; others
have accumulated in the abyss of the ocean, having been formed by
the drifting and engulfing of immense rafts of trees and other
vegetable matter, like those of the Mississippi; others in inland
seas, the successive layers of vegetables having been supplied by
periodical land-floods. There can be no doubt that coal has been,
and may be, produced under all these conditions; and at different
periods, and in various localities, all these causes may have been in
operation. But the great series of ancient coal-formations present
a remarkable uniformity of character, not only throughout Europe,
but also in America and other parts of the world. A coal-field (as
a group of strata of this kind is commonly termed), is generally
composed of a series of layers of coal, clay, shale, and sand, of
variable thicknesses, based on grit or limestone, abounding in marine
shells and corals; and the most remarkable phenomenon is the constant
presence _beneath_ every bed of coal, of a thick stratum of earthy
clay, and of a layer of shale or slaty clay above it. One of the
series of triple deposits of which a coal-field consists, presents
therefore the following characters:--
1. _Under-clay_; the lowermost stratum. This is a tough argillaceous
earth or clay, which on drying becomes of a grey colour, and
very friable; it is occasionally black, from an intermixture of
carbonaceous matter. This bed almost invariably contains an abundance
of _Stigmariæ_ (see Plates XXII. XXIII.), of considerable length,
with their rootlets attached, and which extend in every direction
through the clay (as shown in the figures 1, 2, 6, pp. 199, 201).
These roots commonly lie parallel with the planes of the stratum, and
nearer to the top than to the bottom.
2. _Coal._--A carbonized mass, in which the external forms of the
plants and trees composing it are obliterated, but the internal
structure, in many instances, remains. Large trunks, and stems, and
leaves, are rarely found in it.
3. _The Roof_, or upper bed.--This consists of slaty clay, abounding
in leaves, trunks and branches, fruit, &c.; it includes layers and
nodules of ironstone, inclosing leaves, insects, Crustacea, &c. In
some localities beds of fresh-water shells, in others of marine
shells, are intercalated with the shale; finely laminated clay,
micaceous sand, grit, and pebbles of limestone, sandstone, &c. are
also often interstratified. The principal illustrative specimens of
the leaves, fruit, &c. (as those in Plate XXX. to Plate XXXIV.) are
found in this bed.
Thus an uninterrupted series of strata, in which triple deposits of
this kind are repeated, (often thirty or forty times, and through
a thickness of several thousand feet,) constitutes the predominant
character of the ancient coal formations wherever they have been
explored. The difficulties attending a satisfactory solution of
this problem, are fully stated in the last edition of my Wonders of
Geology (Vol. ii. Lecture vii.), and to that work I must refer the
reader for a more extended consideration of this highly interesting
subject.
[Footnote 104: See Medals of Creation, vol. ii. chap. i.; and
Thoughts on a Pebble, pp. 20, 69.]
VII. Coal.--The numerous fossil plants from the carboniferous strata
that are figured in this work, render it necessary to put the general
reader in possession of a concise view of the nature and mode of
formation of those ancient accumulations of vegetable matter, which
now constitute the beds of mineral fuel termed coal.
Although at the present time no one at all conversant with geology
doubts the vegetable origin of Coal, the period is not distant when
many eminent philosophers were sceptical on this point; and the
truth in this, as in most other questions In natural philosophy,
was established with difficulty. The experiments and observations
of the late Dr. Macculloch mainly contributed to solve the problem
as to the vegetable origin of this substance; and that eminent
geologist successfully traced the transition of vegetable matter
from peat-wood, brown coal, lignite, and jet, to coal, anthracite,
graphite, and plumbago. Nor must the important labours of Mr.
Parkinson in this field of research be forgotten. The first volume of
the "Organic Remains of a former World," which treats of vegetable
fossils, contains much original and valuable information on the
transmutation of vegetable matter, by bituminous fermentation, into
the various mineral substances in which its original nature and
structure are altogether changed and obliterated; and that work may
still be consulted with advantage by the student.
But though the vegetable origin of all coal will not admit of
question, yet evidence of the original structure of the plants or
trees whence it was derived is not always attainable. The most
perfect coal seems to have undergone a complete liquefaction, and
if any portions of the vegetable tissue remain, they appear as
if imbedded in a pure bituminous mass. The slaty coal generally
preserves traces of cellular or vascular tissue, and the spiral
vessels and dotted cells of coniferous trees may often be detected
by the microscope. In many instances the cells are filled with an
amber-coloured resinous substance; in others the organization is so
well preserved, that on the surface of a block of coal cracked by
heat, the vascular tissue, and the dotted glands, may be observed.
Some beds of coal appear to be wholly composed of minute leaves or
disintegrated foliage; for if a mass recently extracted from the
mine be split asunder, the exposed surfaces are found covered with
delicate laminæ of carbonized leaves and fibres matted together;
and flake after flake may be peeled off through a thickness of many
inches, and the same structure be apparent. Rarely are any large
trunks or branches observable in the beds of coal; but the general
appearance of the carboniferous mass is that of an immense deposit of
delicate foliage shed and accumulated in a forest, and consolidated
by great pressure while undergoing that peculiar process by which
vegetable matter is converted into carbon.
The essential conditions for the transmutation of vegetable
substances into coal, appear to be the imbedding of large quantities
of recent vegetables beneath deposits which shall exclude the air,
and prevent the escape of the gaseous elements when released by
decomposition from their organic combination; hence, according as
these conditions have been more or less perfectly fulfilled, coal,
jet, lignite, brown-coal, peat-wood, &c. will be the result.
VIII. Fossil Corals.--The real nature even of recent Corals is in
general so imperfectly understood by the intelligent reader who has
not paid especial attention to the department of natural history
which treats of the class of animated nature termed Zoophytes, that
in describing the Fossil Corals In my Wonders of Geology, I felt
it necessary to devote one Lecture to the consideration of Corals
and Crinoidea, in order to afford a popular exposition of the
structure and economy of these highly Interesting tribes of animal
existence.[105]
[Footnote 105: See Wonders of Geology, vol. ii. Lect. vi. p. 588.]
A very prevalent error regarding their nature Is, that the beautiful
stony substances generally called corals, are fabricated by the
animalcules which inhabit the cells when living, in the same manner
as is the honeycomb of the bee and wasp. This opinion is utterly
erroneous: the coral is secreted by the integuments or membranes with
which when recent it was invested and permeated; in like manner as
are the bones of the skeleton in the higher orders of animals by the
tissues designed for that especial purpose, and wholly without the
cognisance or control of the creature of which they constitute the
internal support.
A general idea of the nature of the compound coral-zoophytes may be
obtained by the examination of the common _Flustra_ or Sea-mat. This
form of polyparia, when taken out of the water, appears to the naked
eye like a patch of fine varnished net-work, adhering to a piece of
sea-weed or stone; when viewed with a magnifying lens of moderate
power, the surface is found beset with pores regularly disposed:
and if the Flustra be examined while immersed in sea-water, its
surface is seen to be invested by a gelatinous substance, and every
pore is the aperture of a cell, whence issues a tube fringed at the
extremity with long tentacula or feelers. These expand, then suddenly
contract, withdraw into the cell, and again issue forth: the whole
surface of the Flustra being studded with the hydra-like animalcules;
each enjoying a distinct existence, the entire group being united
by one common integument or calcareous frame-work. When the Flustra
is exposed to the air, the polypes soon perish, the animal matter
rapidly decomposes, and the calcareous lace-like skeleton alone
remains. In the larger and more compact corals the phenomena are
similar, differing only in degree. In a fossil state, the durable
remains of the corals consist for the most part of the calcareous
frame-work (or polyparium, as it is termed), which often possesses a
crystalline structure; and in some instances is completely transmuted
into silex, as in specimens from Antigua, the Falls of the Ohio, and
from Tisbury in Wiltshire. (See Plate XXXVIII. figs. 12, 13.)
I must refer to the Wonders of Geology for a more extended notice
of fossil corals, and other zoophytes, and will only add that the
calcareous and siliceous spines or spicula, not only of sponges, but
also of Gorgoniæ, and other corals, are often met with in a fossil
state.[106]
[Footnote 106: See Wonders of Geology, vol. ii. Lect. vi. p. 634.]
IX. Cuvier's Discoveries. _The Fossil Quadrupeds of Montmartre._
(Plate LXXII.)--The Palæotheria, Anoplotheria, and other genera of
extinct quadrupeds related to the _Tapir_, whose remains were first
noticed in the gypseous limestone of Montmartre, near Paris, and
which have since been found in many other localities of the same
strata, are familiar to every one, from the just celebrity attached
to the labours of the illustrious Cuvier, who restored as it were
these lost denizens of an earlier world, in their native character
and forms, and distinguished them by names long since become
classical in the sciences which treat of the ancient history of the
earth and its inhabitants.
The gypsum quarries spread over the flanks of Montmartre were many
years since known to contain fossil bones of extinct quadrupeds, and
some of these had been figured and described in 1768 by Guettard,
and afterwards by Pralon, Lamanon, and Parumot: but it was not till
the attention of M. Cuvier was directed to the subject by some
specimens put into his hands by M. Vuarin, that the interest and
importance of these fossils were understood. The curiosity of Baron
Cuvier was so much excited by an inspection of a large collection
of these bones, soon after he had been successfully engaged in the
investigation of the remains of fossil Elephants and Mastodons,
that he immediately began to obtain specimens from the quarries,
and by liberally rewarding the workmen, and by unremitting personal
research, he soon accumulated an immense quantity of bones of all
sorts, belonging to numerous individuals. He now perceived that
a new world was open to his view: and to use his own expressive
language, he found himself in an ancient charnel-house, surrounded
by a confused multitude of mangled skeletons of a great variety of
unknown beings. To arrange each fragment in its proper place, and
restore order to these heterogeneous materials, seemed at first a
hopeless task: but a knowledge of the immutable laws by which the
organization of animal existence is governed, soon enabled him to
assign to each bone, and even fragment, its proper place in the
skeleton; and the forms of beings hitherto unseen by mortal eye
appeared before him. "I cannot," he exclaims, "express my delight in
finding how the application of one principle was instantly followed
by the most triumphant results. The essential character of a tooth
and its relation to the skull being determined, all the other
elements of the fabric immediately fell into their proper places; and
the vertebra, ribs, bones of the legs, thigh, and feet, seemed to
arrange themselves even without my bidding, and in the very manner
I had predicted." The principles of the correlation of structure
which his profound researches in comparative anatomy had enabled
him to establish, conducted to these important results, and laid
the foundation of that science which has since received the name of
Palæontology.[107] The mode of induction adopted by this illustrious
philosopher, has been the mighty instrument by which subsequent
labourers in this department of science have so largely contributed
to our knowledge of the ancient condition of the earth, and of the
structure and economy of the tribes of beings which have successively
dwelt upon it. The examination of the fossil teeth (in Plate LXXII.
figs. 4-9) showed that the animals were herbivorous; and the crown
of the tooth being composed of two or three simple crescents, as in
certain pachydermata, proved that they differed from the ruminants,
which have double crescents, and each four bands of enamel. The
two principal genera first established were the _Palæotherium_ and
_Anoplotherium_. The first approximates to the Tapirs in the number
and disposition of the teeth; the second is remarkable in having no
projecting canines, and in all the teeth forming a continued series,
as in the human race. Remains of both these genera have been found
in the eocene tertiary strata of the Isle of Wight,[108] and on the
coast of Hampshire.
[Footnote 107: A concise exposition of the Cuvierian inductive
philosophy will be found in Wonders of Geology, pp. 137-147.]
[Footnote 108: See my Geological Excursions round the Isle of Wight.
For an account of the fossil animals of Paris, refer to Wonders of
Geology, p. 254.]
X. Fossil Edentata. _Megatherium, and Megalonyx_. (Plates LXXII.
and LXXIII.)--The remains of these and other allied forms of the
extinct gigantic Edentata, which once inhabited South America, occur
in immense quantities throughout the Pampas--those vast plains which
present a sea of waving grass for 900 miles. These plains consist
of alluvial loam and sand, containing fresh-water and marine shells
of existing species; they were evidently once, like Lewes Levels,
a gulf or arm of the sea. Since the publication of Mr. Parkinson's
work, vast numbers of bones have been exhumed, and many most
interesting specimens sent to England by Sir Woodbine Parish, and
Charles Darwin, Esq., in whose charming "Journal of Researches into
the Natural History and Geology of the Countries visited during the
Voyage of H.M.S. Beagle round the World," will be found many highly
graphic notices of the discovery of these remains.[109] Mr. Darwin,
under the head of _Bahia Blanca_,[110] describes the remains of no
less than nine great quadrupeds found imbedded within the space of
200 square yards. They consisted of three heads and other bones
of the _Megatherium_, of enormous dimensions; and bones of the
_Megalonyx_. Of the _Scelidotherium_, an allied animal, Mr. Darwin
obtained an almost perfect skeleton; it must have been as large as a
rhinoceros; in the structure of the head, it approaches nearest the
Cape ant-eater, in other respects it is related to the armadilloes.
Remains of a different species of Mylodon, of another gigantic
edental quadruped, and of a large animal with an osseous dermal coat
in compartments, very like that of the Armadillo. Of this last, which
has been named _Glyptodon_, there is a very fine specimen in the
Hunterian Museum. Teeth and bones of an extinct species of horse,
and of an unknown pachyderm, a huge beast with a long neck like the
camel. Lastly the _Toxodon_ (so named from the remarkable curvature
of the teeth); this is perhaps one of the strangest animals ever
discovered. In size it equals the elephant or megatherium, but the
structure of its teeth shows it to have been intimately related to
the gnawers--the order which at the present day includes the smallest
quadrupeds. In many details it approaches to the pachydermata;
judging from the position of its eyes, it was probably aquatic, like
the Dugong and Manatee, to which it is also allied.
[Footnote 109: Published by Mr. Murray, in one vol. 1845. The
anatomical description of the fossil Edentata brought home by Mr.
Darwin, by Professor Owen, will be found in the "Zoology of the
Voyage of the Beagle."]
[Footnote 110: Mr. Darwin's Journal, chap. v. p. 81.]
The beds containing the above fossil remains, consist of stratified
gravel and reddish mud, and stand only from fifteen to twenty feet
above the level of high water; hence the elevation of the land has
been small since the great quadrupeds wandered over the surrounding
plains; and the external features of the country must then have been
very nearly the same as now.
In another place, Mr. Darwin observes,--"The number of the remains of
these large quadrupeds imbedded in the grand estuary deposit which
forms the Pampas and covers the granitic rocks of Banda Oriental,
must be extraordinarily great. I believe, a straight line drawn in
any direction through the Pampas, would cut through some skeleton
or bones. Besides those which I found during my short excursions, I
heard of many others; and the origin of such names as, 'the stream
of the animal,' 'the hill of the giant,' is obvious. At other times,
I heard of the marvellous property of certain rivers, which had the
power of changing small bones into large; or as some maintained,
the bones themselves grew. As far as I am aware, not one of these
animals perished, as was formerly supposed, in the marshes or
muddy river-beds of the present land, but their bones have been
exposed by the streams intersecting the subaqueous deposit, in
which they were originally imbedded. We may conclude that the whole
area of the Pampas is one wide sepulchre of these extinct gigantic
quadrupeds."[111]
[Footnote 111: Mr. Darwin's Journal, p. 135. The reader interested
in these extraordinary fossil remains should visit the British
Museum, and the Hunterian Museum of the Royal College of Surgeons in
Lincoln's Inn Fields.]