EOCENE FORMATIONS--_continued_.
Subdivisions of the Eocene group in the Paris basin--Gypseous
series--Extinct quadrupeds--Impulse given to geology by Cuvier's
osteological discoveries--Shelly sands called sables moyens--Calcaire
grossier--Miliolites--Calcaire siliceux--Lower Eocene in France--Lits
coquilliers--Sands and plastic clay--English Eocene strata--Freshwater
and fluvio-marine beds--Barton beds--Bagshot and Bracklesham
division--Large ophidians and saurians--Lower Eocene and London Clay
proper--Fossil plants and shells--Strata of Kyson in Suffolk--Fossil
monkey and opossum--Mottled clays and sands below London
Clay--Nummulitic formation of Alps and Pyrenees--Its wide geographical
extent--Eocene strata in the United States--Section at Claiborne,
Alabama--Colossal cetacean--Orbitoid limestone--Burr stone.
From what was said in the two preceding chapters, it has already
appeared that we have in England no true chronological representative of
the Miocene faluns of the Loire, and none of the Upper Eocene group
described in the last chapter. But, when we descend to the middle and
inferior divisions of the Eocene system of France, we find that they
have their equivalents in Great Britain.
MIDDLE EOCENE.--FRANCE.
_Gypseous series_ (2. _a_, Table, p. 175.).--Next below the upper marine
sands of the neighbourhood of Paris, we find a series of white and green
marls, with subordinate beds of gypsum. These are most largely developed in
the central parts of the Paris basin, and, among other places, in the Hill
of Montmartre, where its fossils were first studied by M. Cuvier.
The gypsum quarried there for the manufacture of plaster of Paris occurs as
a granular crystalline rock, and, together with the associated marls,
contains land and fluviatile shells, together with the bones and skeletons
of birds and quadrupeds. Several land plants are also met with, among which
are fine specimens of the fan palm or palmetto tribe (_Flabellaria_). The
remains also of freshwater fish and of crocodiles and other reptiles, occur
in the gypsum. The skeletons of mammalia are usually isolated, often
entire, the most delicate extremities being preserved; as if the carcasses,
clothed with their flesh and skin, had been floated down soon after death,
and while they were still swoln by the gases generated by their first
decomposition. The few accompanying shells are of those light kinds which
frequently float on the surface of rivers, together with wood.
M. Prevost has therefore suggested that a river may have swept away the
bodies of animals, and the plants which lived on its borders, or in the
lakes which it traversed, and may have carried them down into the centre
of the gulf into which flowed the waters impregnated with sulphate of
lime. We know that the Fiume Salso in Sicily enters the sea so charged
with various salts that the thirsty cattle refuse to drink of it. A
stream of sulphureous water, as white as milk, descends into the sea
from the volcanic mountain of Idienne on the east of Java; and a great
body of hot water, charged with sulphuric acid, rushed down from the
same volcano on one occasion, and inundated a large tract of country,
destroying, by its noxious properties, all the vegetation.[191-A] In
like manner the Pusanibio, or "Vinegar River," of Colombia, which rises
at the foot of Purace, an extinct volcano, 7,500 feet above the level of
the sea, is strongly impregnated with sulphuric and muriatic acids and
with oxide of iron. We may easily suppose the waters of such streams to
have properties noxious to marine animals, and in this manner the entire
absence of marine remains in the ossiferous gypsum may be
explained.[191-B] There are no pebbles or coarse sand in the gypsum; a
circumstance which agrees well with the hypothesis that these beds were
precipitated from water holding sulphate of lime in solution, and
floating the remains of different animals.
In this formation the relics of about fifty species of quadrupeds,
including the genera _Paleotherium_, _Anoplotherium_, and others, have been
found, all extinct, and nearly four-fifths of them belonging to a division
of the order _Pachydermata_, which is now represented by only four living
species; namely three tapirs and the daman of the Cape. With them a few
carnivorous animals are associated, among which are a species of fox and
gennet. Of the _Rodentia_, a dormouse and a squirrel; of the _Insectivora_,
a bat; and of the _Marsupialia_ (an order now confined to America,
Australia, and some contiguous islands), an opossum, have been discovered.
Of birds, about ten species have been ascertained, the skeletons of some of
which are entire. None of them are referable to existing species.[192-A]
The same remark applies to the fish, according to MM. Cuvier, and Agassiz,
as also to the reptiles. Among the last are crocodiles and tortoises of the
genera _Emys_ and _Trionyx_.
The tribe of land quadrupeds most abundant in this formation is such as
now inhabits alluvial plains and marshes, and the banks of rivers and
lakes, a class most exposed to suffer by river inundations. Whether the
disproportion of carnivorous animals can be ascribed to this cause, or
whether they were comparatively small in number and dimensions, as in
the indigenous fauna of Australia, when first known to Europeans, is a
point on which it would be rash, perhaps, to offer an opinion in the
present state of our knowledge.
[Illustration: Fig. 162. _Paleotherium magnum._]
The Paleothere, above alluded to, resembled the living tapir in the form of
the head, and in having a short proboscis, but its molar teeth were more
like those of the rhinoceros (see fig. 163.). _Paleotherium magnum_ was of
the size of a horse, 3 or 4 feet high. The annexed woodcut, fig. 162., is
one of the restorations which Cuvier attempted of the outline of the living
animal, derived from the study of the entire skeleton. When the French
osteologist declared in the early part of the present century, that all the
fossil quadrupeds of the gypsum of Paris were extinct, the announcement of
so startling a fact, on such high authority, created a powerful sensation,
and from that time a new impulse was given throughout Europe to the
progress of geological investigation. Eminent naturalists, it is true, had
long before maintained that the shells and zoophytes, met with in many
ancient European rocks, had ceased to be inhabitants of the earth, but the
majority even of the educated classes continued to believe that the species
of animals and plants now contemporary with man, were the same as those
which had been called into being when the planet itself was created. It was
easy to throw discredit upon the new doctrine by asking whether corals,
shells, and other creatures previously unknown, were not annually
discovered? and whether living forms corresponding with the fossils might
not yet be dredged up from seas hitherto unexamined? But from the era of
the publication of Cuvier's Ossements Fossiles, and still more his popular
Treatise called "A Theory of the Earth," sounder views began to prevail. It
was clearly demonstrated that most of the mammalia found in the gypsum of
Montmartre differed even generically from any now existing, and the extreme
improbability that any of them, especially the larger ones, would ever be
found surviving in continents yet unexplored, was made manifest. Moreover,
the non-admixture of a single living species in the midst of so rich a
fossil fauna was a striking proof that there had existed a state of the
earth's surface zoologically unconnected with the present order of things.
[Illustration: Fig. 163. Upper molar tooth of _Paleotherium magnum_ from
Isle of Wight. (Owen's Brit. Foss. p. 317.)
Reduced one-third.]
_Gres de Beauchamp_ (2. _b_, Table, p. 175.).--In some parts of the Paris
basin, sands and marls, called the Gres de Beauchamp, or Sables Moyens,
divide the gypseous beds from the underlying Calcaire grossier. These sands
contain more than 300 species of marine shells, many of them peculiar, but
others common to the underlying marine deposit (No. 2. _c_.).
_Calcaire grossier_ (2. _c_, Table, p. 175.).--The formation called
Calcaire grossier consists of a coarse limestone, often passing into sand.
It contains the greater number of the fossil shells which characterize the
Paris basin. No less than 400 distinct species have been procured from a
single spot near Grignon, where they are embedded in a calcareous sand,
chiefly formed of comminuted shells, in which, nevertheless, individuals in
a perfect state of preservation, both of marine, terrestrial, and
freshwater species, are mingled together. Some of the marine shells may
have lived on the spot; but the _Cyclostoma_ and _Limnea_ must have been
brought thither by rivers and currents, and the quantity of triturated
shells implies considerable movement in the waters.
Nothing is more striking in this assemblage of fossil testacea than the
great proportion of species referable to the genus _Cerithium_ (see fig.
164.). There occur no less than 137 species of this genus in the Paris
basin, and almost all of them in the calcaire grossier. Now the living
_Cerithia_ inhabit the sea near the mouths of rivers, where the waters
are brackish; so that their abundance in the marine strata now under
consideration is in harmony with the hypothesis, that the Paris basin
formed a gulf into which several rivers flowed, the sediment of some of
which gave rise to the beds of clay and lignite before mentioned; while
a distinct freshwater limestone, called calcaire siliceux, which will
presently be described, was precipitated from the waters of others
situated farther to the south.
[Illustration: Fig. 164. Cerithium cinctum.[194-A]]
[4 Illustrations: EOCENE FORAMINIFERA.
Fig. 165. _Calcarina rarispina_, Desh.
_b_. natural size.
_a_, _c_. same magnified.
Fig. 166. _Spirolina stenostoma_, Desh.
B. natural size.
A, C, D. same magnified.
Fig. 167. _Triloculina inflata_, Desh.
_b_. natural size.
_a_, _c_, _d_, same magnified.
Fig. 168. _Clavulina corrugata_, Desh.
_a_. natural size.
_b_, _c_. same magnified.]
In some parts of the calcaire grossier round Paris, certain beds occur of a
stone used in building, and called by the French geologists "Miliolite
limestone." It is almost entirely made up of millions of microscopic
shells, of the size of minute grains of sand, which all belong to the class
Foraminifera. Figures of some of these are given in the annexed woodcut. As
this miliolitic stone never occurs in the Faluns, or Miocene strata of
Brittany and Touraine, it often furnishes the geologist with a useful
criterion for distinguishing the detached Eocene and Miocene formations,
scattered over those and other adjoining provinces. The discovery of the
remains of Paleotherium and other mammalia in some of the upper beds of the
calcaire grossier shows that these land animals began to exist before the
deposition of the overlying gypseous series had commenced.
_Calcaire siliceux_.--This compact siliceous limestone extends over
a wide area. It resembles a precipitate from the waters of mineral
springs, and is often traversed by small empty sinuous cavities.
It is, for the most part, devoid of organic remains, but in some
places contains freshwater and land species, and never any marine
fossils. The siliceous limestone and the calcaire grossier occupy
distinct parts of the Paris basin, the one attaining its fullest
development in those places where the other is of slight thickness.
They also alternate with each other towards the centre of the basin,
as at Sergy and Osny; and there are even points where the two rocks are
so blended together that portions of each may be seen in hand specimens.
Thus, in the same bed, at Triel, we have the compact freshwater
limestone, characterized by its _Limneae_, mingled with the coarse marine
limestone, with its small multilocular shells, or "miliolites,"
dispersed through it in countless numbers. These microscopic testacea
are also accompanied by _Cerithia_ and other shells of the calcaire
grossier. It is very extraordinary that in this instance both kinds of
sediment must have been thrown down together on the same spot, yet each
retains its own peculiar organic remains.
From these facts we may conclude, that while to the north, where the bay
was probably open to the sea, a marine limestone was formed, another
deposit of freshwater origin was introduced to the southward, or at the
head of the bay; for it appears that during the Eocene period, as now, the
ocean was to the north, and the continent, where the great lakes existed,
to the south. From that southern region we may suppose a body of fresh
water to have descended, charged with carbonate of lime and silica, the
water being perhaps in sufficient volume to freshen the upper end of the
bay. The gypseous series (2. _a_, Table, p. 175.), before described, was
once supposed to be entirely subsequent in origin to the two groups, called
calcaire grossier and calcaire siliceux. But M. Prevost has pointed out
that in some localities they alternate repeatedly with both.
The gypsum, with its associated marl and limestone, is in greatest force
towards the centre of the basin, where the calcaire grossier and calcaire
siliceux are less fully developed. Hence M. Prevost infers, that while
those two principal deposits were gradually in progress, the one towards
the north, and the other towards the south, a river descending from the
east may have brought down the gypseous and marly sediment.
It must be admitted, as highly probable, that a bay or narrow sea, 180
miles in length, would receive, at more points than one, the waters of the
adjoining continent. At the same time, we must be prepared to find that
the simultaneous deposition of two or more sets of strata in one basin,
some freshwater and others marine, must have produced very complex results.
But, in proportion as it is more difficult in these cases to discover any
fixed order of superposition in the associated mineral masses, so also is
it more easy to explain the manner of their origin, and to reconcile their
relations to the agency of known causes. Instead of the successive
irruptions and retreats of the sea, and changes in the chemical nature of
the fluid, and other speculations of the earlier geologists, we are now
simply called upon to imagine a gulf, into one extremity of which the sea
entered, and at the other a large river, while other streams may have
flowed in at different points, whereby an indefinite number of alternations
of marine and freshwater beds would be occasioned.
LOWER EOCENE, FRANCE.
_Lits coquilliers_ (3. _a_, Table, p. 175.).--Below the calcaire grossier
are extensive deposits of sand, in the upper parts of which some marine
beds, called "lits coquilliers," occur, in which M. d'Archiac has
discovered 200 species of shells. Many of these are peculiar, but the
larger portion appear to agree with species of the calcaire grossier, so
that the line of demarcation usually adopted between the French Lower and
Middle Eocene formations, seems not to be very strongly drawn. _Sands and
plastic clay_ (3. _b_, Table, p. 175.)--At the base of the tertiary system
in France are extensive deposits of sands, with occasional beds of clay
used for pottery, and called "argile plastique." Fossil oysters (_Ostrea
bellovacina_) abound in some places, and in others there is a mixture of
fluviatile shells, such as _Cyrena cuneiformis_ (fig. 187. p. 204.),
_Melania inquinata_ (fig. 188.), and others, frequently met with in beds
occupying the same position in the valley of the Thames. Layers of lignite
also accompany the inferior clays and sands.
Immediately upon the chalk at the bottom of all the tertiary strata
there is often a conglomerate or breccia of rolled and angular chalk
flints, cemented by siliceous sand. These beds appear to be of littoral
origin, and imply the previous emergence of some portions of the chalk,
and its waste by denudation.
[Illustration: Fig. 169. _Cardium porulosum_. Paris and London basins.]
The lower sandy beds of the Paris basin are often called the sands of the
Soissonais, from a district so named 50 miles N.E. of Paris. One of the
shells of the formation is adduced by M. Deshayes as an example of the
changes which certain species underwent in the successive stages of their
existence. It seems that different varieties of the _Cardium porulosum_ are
characteristic of different formations. In the Lower Eocene of the
Soissonais this shell acquires but a small volume, and has many
peculiarities, which disappear in the lowest beds of the calcaire grossier.
In these the shell attains its full size, and many distinctive characters,
which are again modified in the uppermost beds of the calcaire grossier;
and these last modifications of form are preserved throughout the whole of
the "upper marine" (or Upper Eocene) series.[197-A]
ENGLISH EOCENE FORMATIONS.
The Eocene areas of Hampshire and London are delineated in the map
(fig. 153. p. 174.).
The following table will show the succession of the principal deposits
found in our island. The true place of the Bagshot sands, in this
series, was never accurately ascertained till Mr. Prestwich published,
in 1847, his classification of the English Eocene strata, dividing them
into three principal formations, in which the Bagshot sands occupied
the central place.[197-B]
Localities.
1. Upper Eocene. Wanting in Great Britain.
{ _a._ Freshwater and Headon Hill, Isle of
{ fluvio-marine beds. Wight; and Hordwell
{ Cliff, Hants.
2. Middle Eocene { _b._ Barton beds. Barton Cliff, Hants.
{ _c._ Bagshot and Bracklesham Bagshot Heath, Surrey;
{ sands and clays. Bracklesham Bay,
{ Sussex.
{ _a._ London Clay Proper, Highgate Hill,
{ and Bognor beds. Middlesex; I. of
{ Sheppey; Bognor,
3. Lower Eocene { Sussex.
{ _b._ Mottled and Plastic Newhaven, Sussex;
{ clays and sands. Reading, Berks;
{ Woolwich, Kent.
[Illustration: Fig. 170. _Lymnea longiscata._
Freshwater Eocene strata, Isle of Wight.]
_Freshwater beds_ (2. _a_, Table, p. 175.).--In the northern part of the
Isle of Wight, beds of marl, clay, and sand, and a friable limestone,
containing freshwater shells, are seen, containing shells of the genera
_Lymnea_ (see fig. 170.), _Planorbis_, _Melanopsis_, _Cyrena_, &c., several
of them of the same species as those occurring in the Eocene beds of the
Paris basin. Gyrogonites, also, or seed-vessels of _Chara_, exhibiting a
similar specific identity, occur. At Headon Hill, on the western side of
the island, where these beds are seen in the sea-cliffs, some of the strata
contain a few marine and estuary shells, such as _Cytheraea_, _Corbula_,
&c., showing a temporary occupation of the area by brackish or salt water,
after which the river or a lake seems again to have prevailed. A species
of fan-palm, _Flabellaria Lamanonis_, Brong., like one which characterizes
the Parisian Eocene beds, has been recently detected by Dr. Mantell in this
formation, in Whitecliff Bay, at the eastern end of the island.
Several of the species of extinct quadrupeds already alluded to as
characterizing the gypsum of Montmartre have been discovered by Messrs.
Pratt and Fox, in the Isle of Wight, chiefly at Binstead, near Ryde, as
_Palaeotherium magnum_, _P. medium_, _P. minus_, _P. minimum_, _P. curtum_,
_P. crassum_, also _Anoplotherium commune_, _A. secundarium_, _Dichobune
cervinum_, and _Chaeropotamus Cuvieri_. In Hordwell cliff, also on the
Hampshire coast, several of these species, with other quadrupeds of new
genera, such as _Paloplotherium_, Owen, have been met with; and remains of
a remarkable carnivorous genus, _Hyaenodon_. These fossils are accompanied
by the bones of _Trionyx_, and other tortoises, and by two land snakes of
the genus _Paleryx_, Owen, from 3 to 4 feet long, also a species of
crocodile, and an alligator. Among other fossils collected by Lady
Hastings, Sir Philip Egerton has recognized the well-known gar or bony pike
of the American rivers, a ganoid fish of the genus _Lepidotus_, with its
hard shining scales. The shells of Hordwell are similar to those of the
freshwater beds of the Isle of Wight, and among them are a few specifically
undistinguishable from recent testacea, as _Paludina lenta_ and _Helix
labyrinthica_, the latter discovered by Mr. S. Wood, and identified with an
existing N. American helix.
The white and green marls of this freshwater series in Hampshire, and some
of the accompanying limestones, often resemble those of France in mineral
character and colour in so striking a manner, as to suggest the idea that
the sediment was derived from the same region, or produced
contemporaneously under very similar geographical circumstances.
_Barton beds._--Both in the cliffs of Headon Hill and Hordwell, already
mentioned, the freshwater series rests on a mass of pure white sand without
fossils, and this is seen in Barton Cliff to overlie a marine deposit, in
which 209 species of testacea have been found. More than half of these are
peculiar; and, according to Mr. Prestwich, only 11 of them common to the
London Clay proper, being in the proportion of only 5 per cent. On the
other hand, 70 of them agree with the _calcaire grossier_ shells. As this
is the newest purely marine bed of the Eocene series known in England, we
might have expected that some of its peculiar fossils would be found to
agree with the upper Eocene strata described in the last chapter, and
accordingly some identifications have been cited with testacea, both of the
Berlin and Belgian strata. It is nearly a century since Brander published,
in 1766, an account of the organic remains collected from these cliffs, and
his excellent figures of the shells then deposited in the British Museum
are justly admired by conchologists for their accuracy.
_Bagshot Sands_ (2. _c_, Table, p. 197.).--These beds, consisting
chiefly of siliceous sand, occupy extensive tracts round Bagshot, in
Surrey, and in the New Forest, Hampshire. They succeed next in
chronological order, and may be separated into three divisions, the
upper and lower consisting of light yellow sands, and the central of
dark green sands and brown clays, the whole reposing on the London clay
proper.[199-A] Although the Bagshot beds are usually devoid of fossils,
they contain marine shells in some places, among which _Venericardia
planicosta_ (see fig. 171.) is abundant, with _Turritella sulcifera_ and
_Nummulites laevigatus_. (See fig. 174. p. 200.)
[Illustration: Fig. 171. _Venericardia planicosta_, Lamck.
_Cardita planicosta_, Deshayes.]
At Bracklesham Bay, near Chichester, in Sussex, the characteristic shells
of this member of the Eocene series are best seen; among others, the huge
_Cerithium giganteum_, so conspicuous in the calcaire grossier of Paris,
where it is sometimes 2 feet in length. The volutes and cowries of this
formation, as well as the lunulites and other corals, seem to favour the
idea of a warm climate having prevailed, which is borne out by the
discovery of a serpent _Palaeophis typhaeus_, exceeding, according to Mr.
Owen, 20 feet in length, and allied to the Boa, Python, Coluber, and
Hydrus. The compressed form and diminutive size of certain caudal vertebrae
indicate so much analogy with Hydrus as to induce the Hunterian professor
to pronounce the extinct ophidian to have been marine.[199-B] He had
previously combated with so much success the evidence advanced, to prove
the existence in the Northern Ocean of sea-serpents in our own times, that
he will not be suspected of any undue bias in contending for their former
existence in the British Eocene seas. The climate, however, of the Middle
Eocene period was evidently far more genial; and amongst the companions of
the sea-serpent of Bracklesham was an extinct Gavial (_Gavialis Dixoni_,
Owen), and numerous fish, such as now frequent the seas of warm latitudes,
as the sword-fish (see fig. 172. p. 200.) and gigantic rays of the genus
Miliobates. (See fig. 173.)
Out of 193 species of testacea procured from the Bagshot and Bracklesham
beds in England, 126 occur in the French calcaire grossier. It was
clearly, therefore, coeval with that part of the Parisian series more
nearly than with any other. The _Nummulites laevigatus_ (see fig. 174.),
a fossil characteristic of the lower beds of the calcaire grossier,
is abundant at Bracklesham.
[Illustration: Fig. 172. Prolonged premaxillary bone or "sword" of
a fossil sword-fish (_Caelorhynchus_). Bracklesham. Dixon's Fossils
of Sussex, pl. 8.]
[Illustration: Fig. 173. Dental plates of _Myliobates Edwardsi_.
Bracklesham Bay. Ibid. pl. 8.]
[Illustration: Fig. 174. _Nummulites_ (_Nummularia_) _laevigatus._
Bracklesham. Ibid. pl. 8.
_a._ section of the nummulite.
_b._ group, with an individual showing the exterior of the shell.]
_London clay proper_ (3. _a_, Table, p. 197.).--This formation underlies
the preceding, and consists of tenacious brown and blueish grey clay, with
layers of concretions called septaria, which abound chiefly in the brown
clay, and are obtained in sufficient numbers from the cliffs near Harwich,
and from shoals of the Essex coast, to be used for making Roman cement. The
principal localities of fossils in the London clay are Highgate Hill, near
London, the island of Sheppey, and Bognor in Hampshire. Out of 133 fossil
shells, Mr. Prestwich found only 20 to be common to the calcaire grossier
(from which 600 species have been obtained), while 33 are common to the
lits coquilliers (p. 196.), in which only 200 species are known in France.
We may presume, therefore, that the London clay proper is older than the
calcaire grossier. This may perhaps remove a difficulty which M. Adolphe
Brongniart has experienced when comparing the Eocene Flora of the
neighbourhoods of London and Paris. The fossil species of the island of
Sheppey, he observes, indicate a much more tropical climate than the Eocene
Flora of France, which has been derived principally from the "gypseous
series." The latter resembles the vegetation of the borders of the
Mediterranean rather than that of an equatorial region.
Mr. Bowerbank, in a valuable publication on the fossil fruits and seeds of
the island of Sheppey, near London, has described no less than thirteen
fruits of palms of the recent type _Nipa_, now only found in the Molucca
and Philippine islands. (See fig. 175.) These plants are allied to the
cocoa-nut tribe on the one side, and on the other to the _Pandanus_, or
screw-pine. Species of cocoa-nuts are also met with, and other kinds of
palms; also three species of _Anona_, or custard-apple; cucurbitaceous
fruits, also (the gourd and melon family), are in considerable abundance.
Fruits of various species of _Acacia_ are in profusion; and, although less
decidedly tropical, imply a warm climate.
[Illustration: Fig. 175. _Nipadites ellipticus._ Bow. Fossil
palm of Sheppey.]
The contiguity of land may be inferred not only from these vegetable
productions, but also from the teeth and bones of crocodiles and turtles,
since these creatures, as Mr. Conybeare has remarked, must have resorted to
some shore to lay their eggs. Of turtles there were numerous species
referred to extinct genera, and, for the most part, not equal in size to
the largest living tropical turtles. A snake, which must have been 13 feet
long, of the genus _Palaeophis_ before mentioned, has also been described by
Mr. Owen from Sheppey, of a different species from that of Bracklesham. A
true crocodile, also, _Crocodilus toliapicus_, and another Saurian more
nearly allied to the gravial, accompany the above fossils. A bird allied to
the vultures, and a quadruped of the new genus _Hyracotherium_, allied to
the Hyrax, Hog, and Chaeropotamus, are also among the additions made of late
years to the palaeontology of this division.
[3 Illustrations: FOSSIL SHELLS OF THE LONDON CLAY.
Fig. 176. _Mitra scabra_.
Fig. 177. _Rostellaria macroptera_, Sow. One-third of nat. size.
Fig. 178. _Crassatella sulcata._]
The marine shells of the London clay confirm the inference derivable from
the plants and reptiles of a high temperature. Thus, many species of
_Conus_, _Mitra_, and _Voluta_ occur, a large _Cypraea_, a very large
_Rostellaria_, and shells of the genera _Terebellum_, _Cancellaria_,
_Crassatella_, and others, with four or more species of _Nautilus_ (see
fig. 182.) and other cephalopoda of extinct genera, one of the most
remarkable of which is the _Belosepia_.[202-A] (See fig. 183.)
[Illustration: Fig. 179. _Nautilus centralis._]
[Illustration: Fig. 180. _Voluta athleta._]
[Illustration: Fig. 181. _Terebellum fusiforme._]
[Illustration: Fig. 182. _Aturia zigzag._ Bronn. Syn. _Nautilus zigzag._
Sow. London clay. Sheppey.]
[Illustration: Fig. 183. _Belosepia sepiodea_, De Blainv.
London clay. Sheppey.]
The above shells are accompanied by a sword-fish (_Tetrapterus priscus_,
Agassiz), about 8 feet long, and a saw-fish (_Pristis bisulcatus_, Ag.),
about 10 feet in length; genera now foreign to the British seas. On the
whole, no less than 50 species of fish have been described by
M. Agassiz from these beds in Sheppey, and they indicate, in his
opinion, a warm climate.
[Illustration: Fig. 184. Molar of monkey (_Macacus_).]
_Strata of Kyson in Suffolk._--At Kyson, a few miles east of Woodbridge, a
bed of Eocene clay, 12 feet thick, underlies the red crag. Beneath it is a
deposit of yellow and white sand, of considerable interest, in consequence
of many peculiar fossils contained in it. Its geological position is
probably the lowest part of the London clay proper. In this sand has been
found the first example of a fossil quadrumanous animal discovered in Great
Britain, namely, the teeth and part of a jaw, shown by Mr. Owen to belong
to a monkey of the genus _Macacus_ (see fig. 184.). The mammiferous
fossils, first met with in the same bed, were those of an opossum
(_Didelphys_) (see fig. 185.), and an insectivorous bat (fig. 186.),
together with many teeth of fishes of the shark family. Mr. Colchester in
1840 obtained other mammalian relics from Kyson, among which Mr. Owen has
recognized several teeth of the genus _Hyracotherium_, and the vertebrae of
a large serpent, probably a _Palaeophis_. As the remains both of the
_Hyracotherium_ and _Palaeophis_ were afterwards met with in the London
clay, as before remarked, these fossils confirmed the opinion previously
entertained, that the Kyson sand belongs to the Eocene period. The
_Macacus_, therefore, constitutes the first example of any quadrumanous
animal found in strata as old as the Eocene, or so far from the equator as
lat. 52 deg. N. It was not until after the year 1836 that the existence of any
fossil quadrumana was brought to light. Since that period they have been
found in France, India, and Brazil.
[Illustration: Fig. 185. Molar tooth and part of jaw of opossum.
From Kyson.[203-A]]
[Illustration: Fig. 186. Molars of insectivorous bats, twice nat. size.
From Kyson, Suffolk.]
_Mottled or Plastic Clays_, _&c._ (3. _b_, Table, p. 197.).--No
formations can be more dissimilar on the whole in mineral character than
the Eocene deposits of England and Paris; those of our own island being
almost exclusively of mechanical origin,--accumulations of mud, sand,
and pebbles; while in the neighbourhood of Paris we find a great
succession of strata composed of a coarse white limestone, and compact
siliceous limestone with beds of crystalline gypsum and siliceous
sandstone, and sometimes pure flint used for millstones. Hence it is by
no means an easy task to institute an exact comparison between the
various members of the English and French series, and to settle their
respective ages. It is clear that a continual change was going on in the
fauna and flora by the coming in of new species and the dying out of
others; and contemporaneous changes of geographical conditions were also
in progress in consequence of the rising and sinking of the land and
bottom of the sea. A particular subdivision, therefore, of time was
occasionally represented in one area by land, in another by an estuary,
in a third by the sea, and even where the conditions were in both
areas of a marine character, there was often shallow water in one,
and deep sea in another, producing a want of agreement in the state
of animal life.
At the commencement, however, of the Eocene formations in France and
England, we find an exception to this rule, for a marked similarity of
mineral character reigns in the lowest division, whether in the basins
of Paris, Hampshire, or London. This uniformity of aspect must be seen
in order to be fully appreciated, since the beds consist simply of sand,
mottled clays, and well-rolled flint pebbles, derived from the chalk,
and varying in size from that of a pea to an egg. These strata may be
seen at Reading, at Blackheath, near London, and at Woolwich. In some
of the lowest of them, banks of oysters are observed, consisting of
_Ostrea bellovicina_, so common in France in the same relative position,
and _Ostrea edulina_, scarcely distinguishable from the living eatable
species. In this formation at Bromley, Dr. Buckland found one large
pebble to which five full-grown oysters were affixed, in such a manner
as to show that they had commenced their first growth upon it, and
remained attached to it through life.
In several places, as at Woolwich on the Thames, at Newhaven in Sussex, and
elsewhere, a mixture of marine and freshwater testacea distinguishes this
member of the series. Among the latter, _Melania inquinata_ (see fig. 188.)
and _Cyrena cuneiformis_ are very common. They probably indicate points
where rivers entered the Eocene sea.
[Illustration: Fig. 187. _Cyrena cuneiformis_, Min. Con. Natural size.]
[Illustration: Fig. 188. _Melania inquinata_, Des. Nat. size.
Syn. _Cerithium melanoides_, Min. Con.]
With us as in France, clay of this formation is used in some places, as
near Poole in Dorsetshire, for pottery; and hence the name of plastic clay
was adopted for the group by Mr. T. Webster. Lignite also is associated
with it in some spots, as in the Paris basin.
Before the minds of geologists had become familiar with the theory of the
gradual sinking of the land, and its conversion into sea at different
periods, and the consequent change from shallow to deep water, the
freshwater and littoral character of this inferior group appeared strange
and anomalous. After passing through many hundred feet of London clay,
proved by its fossils to have been deposited in salt water of considerable
depth, we arrive at beds of fluviatile origin. Thick masses, also, of
shingle indicate the proximity of land, where the flints of the chalk were
rolled into sand and pebbles, and spread continuously over wide spaces, as
in the Isle of Wight, in the south of Hampshire, and near London, always
appearing at the bottom of the Eocene series. It may be asked why they did
not constitute simply a narrow littoral zone, such as we might look for in
strata formed at a moderate distance from the shore. In answer to this
inquiry, the student must be reminded, that wherever a gently-sloping land
is gradually sinking and becoming submerged, shingle may be heaped up
successively over a wide area, although marine currents have no power of
dispersing it simultaneously over a large space. In such cases it is not
the shingle which recedes from the coast, but the coast which recedes from
the shingle, which is formed one mass after another as often as successive
portions of the land are converted into sea and others into a sea beach.
The London area appears to have been upraised before that of Hampshire, so
that it never became the receptacle of the Barton clays, nor of the
overlying fluvio-marine and freshwater beds of Hordwell and the north part
of the Isle of Wight. On the other hand, the Hampshire Eocene area seems to
have emerged before that of Paris, so that no marine beds of the Upper
Eocene era were ever thrown down in Hampshire.
_Nummulitic formation of the Alps and Pyrenees._--It has long been
matter of controversy, whether the nummulitic rocks of the Alps and
Pyrenees should be regarded as Eocene or Cretaceous; but the number of
geologists of high authority who regard this important group as
belonging to the lowest tertiary system of Europe has for many years
been steadily increasing. The late M. Alex. Brongniart first declared
the specific identity of many of the shells of this formation with those
of the marine strata near Paris, although he obtained them from the
summit of the Diablerets, one of the loftiest of the Swiss Alps, which
rises more than 10,000 feet above the level of the sea.
Deposits of the same age, found on the flanks of the Pyrenees, contain also
a great number of shells common to the Paris and London areas, and three or
four species only which are common to the cretaceous formation.
The calcareous division consists often of a compact crystalline marble,
full of nummulites (see fig. 189.), shells of the class _Foraminifera_.
[Illustration: Fig. 189. _Nummulites_. Peyrehorade, Pyrenees.
_a._ external surface of one of the nummulites, of which longitudinal
sections are seen in the limestone.
_b._ transverse section of same.]
The nummulitic limestone of the Alps is often of great thickness, and is
immediately covered by another series of strata of dark-coloured slates,
marls, and fucoidal sandstones, to the whole of which the provincial name
of "flysch" has been given in parts of Switzerland. The researches of Sir
Roderick Murchison in the Alps in 1847 enable us to refer the whole of
these beds to the Eocene period, and it seems probable that they most
nearly coincide in age with the Lower Eocene. They enter into the disturbed
and loftiest portions of the Alpine chain, to the elevation of which they
enable us therefore to assign a comparatively modern date.
The nummulitic formation, with its characteristic fossils, plays a far more
conspicuous part than any other tertiary group in the solid framework of
the earth's crust, whether in Europe, Asia, or Africa. It often attains a
thickness of many thousand feet, and extends from the Alps to the
Apennines. It is found in the Carpathians, and in full force in the north
of Africa, as, for example, in Algeria and Morocco. It has also been traced
from Egypt into Asia Minor, and across Persia by Bagdad to the mouths of
the Indus. It occurs not only in Cutch, but in the mountain ranges which
separate Scinde from Persia, and which form the passes leading to Caboul;
and it has been followed still farther eastward into India.
Some members of this lower tertiary formation in the central Alps,
including even the superior strata called _flysch_, have been converted
into crystalline rocks, and changed into saccharoid marble, quartz,
rock, and mica-schist.[206-A]
EOCENE STRATA IN THE UNITED STATES.
In North America the Eocene formations occupy a large area bordering the
Atlantic, which increases in breadth and importance as it is traced
southwards from Delaware and Maryland to Georgia and Alabama. They also
occur in Louisiana and other states both east and west of the valley of the
Mississippi. At Claiborne in Alabama no less than four hundred species of
marine shells, with many echinoderms and teeth of fish, characterize one
member of this system. Among the shells the _Cardita planicosta_, before
mentioned (fig. 171. p. 199.), is in abundance; and this fossil, and some
others identical with European species, or very nearly allied to them, make
it highly probable that the Claiborne beds agree in age with the central or
Bracklesham group of England, and the calcaire grossier of Paris.[206-B]
Higher in the series is a remarkable calcareous rock, formerly called "the
nummulite limestone," from the great number of discoid bodies resembling
nummulites which it contains, fossils now referred by A. d'Orbigny to the
genus _Orbitoides_, which has been demonstrated by Dr. Carpenter to belong
to the Foraminifera.[206-C] The following section will enable the reader to
understand the position of the three subdivisions of the series, Nos. 1,
2, and 3., the relations of which I ascertained in Clarke County, between
the rivers Alabama and Tombeckbee.
[Illustration: Fig. 190. Cross section.
1. Sand, marl, &c., with numerous fossils. }
2. White or rotten limestone, with _Zeuglodon_. } Eocene.
3. Orbitoidal, or so called nummulitic limestone. }
4. Overlying formation of sand and clay without fossils. Age unknown.]
The lowest set of strata, No. 1., having a thickness of more than 100
feet, comprise marly beds, in which the _Ostrea sellaeformis_ occurs, a
shell ranging from Alabama to Virginia, and being a representative form
of the _Ostrea flabellula_ of the Eocene group of Europe. In others beds
of No. 1., two European shells, _Cardita planicosta_, before mentioned,
and _Solarium canaliculatum_ are found, with a great many other species
peculiar to America. Numerous corals, also, and the remains of placoid
fish and of rays occur, and the "swords," as they are called, of sword
fishes, all bearing a great generic likeness to those of the Eocene
strata of England and France.
No. 2. (fig. 190.) is a white limestone, sometimes soft and argillaceous,
but in parts very compact and calcareous. It contains several peculiar
corals, and a large Nautilus allied to _N. zigzag_, also in its upper bed a
gigantic cetacean, called _Zeuglodon_ by Owen.[207-A]
[2 Illustrations: _Zeuglodon cetoides_, Owen. _Basilosaurus_, Harlan.]
Fig. 191. Molar tooth, natural size.]
Fig. 192. Vertebra, reduced.]
The colossal bones of this cetacean are so plentiful in the interior of
Clarke County as to be characteristic of the formation. The vertebral
column of one skeleton found by Dr. Buckley at a spot visited by me,
extended to the length of nearly 70 feet, and not far off part of another
backbone nearly 50 feet long was dug up. I obtained evidence, during a
short excursion, of so many localities of this fossil animal within a
distance of 10 miles, as to lead me to conclude that they must have
belonged to at least forty distinct individuals.
Mr. Owen first pointed out that the huge animal was not reptilian, since
each tooth was furnished with double roots (see fig. 191.), implanted in
corresponding double sockets; and his opinion of the cetacean nature of
the fossil was afterwards confirmed by Dr. Wyman and Professor R. W.
Gibbes. That it was an extinct species of the whale tribe has since been
placed beyond all doubt by the discovery of the entire skull of another
fossil of the same family, found to have the double occipital condyles
only met with in mammals, and the convoluted tympanic bones which are
characteristic of cetaceans.
Near the junction of No. 2. and the incumbent limestone, No. 3., next to be
mentioned, are strata characterized by the following shells: Spondylus
dumosus (_Plagiostoma dumosum_, Morton), _Pecten Poulsoni_, _Pecten
perplanus_, and _Ostrea cretacea_.
No. 3. (fig. 190.) is a white limestone, for the most part made up of the
_Orbitoides_ of d'Orbigny before mentioned (p. 206.), formerly supposed to
be a nummulite, and called _N. Mantelli_, mixed with a few lunulites and
small corals and shells.[208-A] The origin of this cream-coloured soft
stone, like that of our white chalk, which it much resembles, is, I
believe, due to the decomposition of the orbitoides. The surface of the
country where it prevails is sometimes marked by the absence of wood, like
our chalk downs, or is covered exclusively by the _Juniperus Virginiana_,
as certain chalk districts in England by yew trees and juniper.
Some of the shells of this limestone are common to the Claiborne beds, but
many of them are peculiar.
It will be seen in the section (fig. 190. p. 155.) that the strata, Nos. 1,
2, 3., are, for the most part, overlaid by a dense formation of sand or
clay without fossils. In some points of the bluff or cliff of the Alabama
river, at Claiborne, the beds Nos. 1, 2., are exposed nearly from top to
bottom, whereas at other points the newer formation, No. 4., occupies the
face of nearly the whole cliff. The age of this overlying mass has not yet
been determined, as it has hitherto proved destitute of organic remains.
The burr-stone strata of the Southern States contain so many fossils
agreeing with those of Claiborne, that it doubtless belongs to the same
part of the Eocene group, though I was not fortunate enough to see the
relations of the two deposits in a continuous section. Mr. Tuomey considers
it as the lower portion of the series. It may, perhaps, be a form of the
Claiborne beds in places where lime was wanting, and where silex, derived
from the decomposition of felspar, predominated. It consists chiefly of
slaty clays, quartzose sands, and loam, of a brick red colour, with layers
of chert or burr-stone, used in some places for millstones.
FOOTNOTES:
[191-A] Leyde Magaz. voor Wetensch Konst en Lett., partie v. cahier i. p.
71. Cited by Rozet, Journ. de Geologie, tom. i. p. 43.
[191-B] M. C. Prevost, Submersions Iteratives, &c. Note 23.
[192-A] Cuvier, Oss. Foss., tom. iii. p. 255.
[194-A] This species is found both in the Paris and London basins.
[197-A] Coquilles caracterist. des Terrains, 1831.
[197-B] Quarterly Geol. Journal, vol. iii. p. 353.
[199-A] Prestwich, Quart. Geol. Journ. vol. iii. p. 386.
[199-B] Palaeont. Soc. Monograph. Rept. pt. ii. p. 61.
[202-A] For description of Eocene Cephalopoda, see Monograph by F. E.
Edwards, Palaeontograph. Soc. 1849.
[203-A] Annals of Nat. Hist. vol. iv. No. 23. Nov. 1839.
[206-A] Murchison, Quart. Journ. of Geol. Soc. vol. v., and Lyell, vol. vi.
1850. Anniversary Address.
[206-B] See paper by the author, Quart. Journ. Geol. Soc. vol. iv, p. 12.;
and Second Visit to the U. S. vol. ii. p. 59.
[206-C] Quart. Journ. Geol Soc. vol. vi. p. 32.
[207-A] See Memoir by R. W. Gibbes, Journ. of Acad. Nat. Sci. Philad.
vol. i. 1847.
[208-A] Lyell, Quart. Journ. Geol. Soc. 1847, vol. iv. p. 15.