OLDER PLIOCENE AND MIOCENE FORMATIONS.
Strata of Suffolk termed Red and Coralline crag--Fossils, and
proportion of recent species--Depth of sea and climate--Reference of
Suffolk crag to the older Pliocene period--Migration of many species
of shells southwards during the glacial period--Fossil whales--Sub-
apennine beds--Asti, Sienna, Rome--Miocene formations--Faluns of
Touraine--Depth of sea and littoral character of fauna--Tropical
climate implied by the testacea--Proportion of recent species of
shells--Faluns more ancient than the Suffolk crag--Miocene strata of
Bordeaux and Piedmont--Molasse of Switzerland--Tertiary strata of
Lisbon--Older Pliocene and Miocene formations in the United
States--Sewalik Hills in India.
The older Pliocene strata, which next claim our attention, are chiefly
confined, in Great Britain, to the eastern part of the county of Suffolk,
where, like the Norwich beds already described, they are called "Crag," a
provincial name given particularly to those masses of shelly sand which
have been used from very ancient times in agriculture, to fertilize soils
deficient in calcareous matter. The relative position of the "red crag" in
Essex to the London clay, may be understood by reference to the
accompanying diagram (fig. 142.).
[Illustration: Fig. 142. Cross section.]
These deposits, judging by the shells which they contain, appear, according
to Professor Edward Forbes, to have been formed in a sea of moderate depth,
generally from 15 to 25 fathoms deep, although in some few spots perhaps
deeper. But they may, nevertheless, have been accumulated at the distance
of 40 or 50 miles from land.
The Suffolk crag is divisible into two masses, the upper of which has been
termed the Red, and the lower the Coralline Crag.[162-A] The upper deposit
consists chiefly of quartzose sand, with an occasional intermixture of
shells, for the most part rolled, and sometimes comminuted. The lower or
Coralline crag is of very limited extent, ranging over an area about 20
miles in length, and 3 or 4 in breadth, between the rivers Alde and Stour.
It is generally calcareous and marly--a mass of shells and small corals,
passing occasionally into a soft building stone. At Sudbourn, near Orford,
where it assumes this character, are large quarries, in which the bottom of
it has not been reached at the depth of 50 feet. At some places in the
neighbourhood, the softer mass is divided by thin flags of hard limestone,
and corals placed in the upright position in which they grew.
The Red crag is distinguished by the deep ferruginous or ochreous colour of
its sands and fossils, the Coralline by its white colour. Both formations
are of moderate thickness; the red crag rarely exceeding 40, and the
coralline seldom amounting to 20, feet. But their importance is not to be
estimated by the density of the mass of strata or its geographical extent,
but by the extraordinary richness of its organic remains, belonging to a
very peculiar type, which seems to characterize the state of the living
creation in the north of Europe during the older Pliocene era.
For a large collection of the fish, echinoderms, shells, and corals of the
deposits in Suffolk, we are indebted to the labours of Mr. Searles Wood. Of
testacea alone he has obtained from 230 species from the Red, and 345 from
the Coralline crag, about 150 being common to each. The proportion of
recent species in the new group is considered by Mr. Wood to be about
70[162-B] per cent., and that in the older or coralline about 60. When I
examined these shells of Suffolk in 1835, with the assistance of Dr. Beck,
Mr. George Sowerby, Mr. Searles Wood, and other eminent conchologists, I
came to the opinion that the extinct species predominated very decidedly in
number over the living. Recent investigations, however, have thrown much
new light on the conchology of the Arctic, Scandinavian, British, and
Mediterranean Seas. Many of the species formerly known only as fossils of
the Crag, and supposed to have died out, have been dredged up in a living
state from depths not previously explored. Other recent species, before
regarded as distinct from the nearest allied Crag fossils, have been
observed, when numerous individuals were procured, to be liable to much
greater variation, both in size and form, than had been suspected, and thus
have been identified. Consequently, the Crag fauna has been found to
approach much more nearly to the recent fauna of the Northern, British, and
Mediterranean Seas than had been imagined. The analogy of the whole group
of testacea to the European type is very marked, whether we refer to the
large development of certain genera in number of species or to their size,
or to the suppression or feeble representation of others. The indication
also afforded by the entire fauna of a climate not much warmer than that
now prevailing in corresponding latitudes, prepares us to believe that they
are not of higher antiquity than the Older Pliocene era.[163-A]
[Illustration: Fig. 143. Section near Ipswich, in Suffolk.
_a._ Red crag.
_b._ Coralline crag.
_c._ London clay.]
The position of the red crag in Essex to the subjacent London clay and
chalk has been already pointed out (fig. 142.). Whenever the two
divisions are met with in the same district, the red crag lies
uppermost; and, in some cases, as in the section represented in fig.
143., it is observed that the older or coralline mass _b_ had suffered
denudation before the newer formation _a_ was thrown down upon it. At D
there is not only a distinct cliff, 8 or 10 feet high, of coralline
crag, running in a direction N.E. and S.W., against which the red crag
abuts with its horizontal layers; but this cliff occasionally overhangs.
The rock composing it is drilled everywhere by _Pholades_, the holes
which they perforated having been afterwards filled with sand and
covered over when the newer beds were thrown down. As the older
formation is shown by its fossils to have accumulated in a deeper sea
(15, and sometimes 25, fathoms deep or more), there must no doubt have
been an upheaval of the sea-bottom before the cliff here alluded to was
shaped out. We may also conclude that so great an amount of denudation
could scarcely take place, in such incoherent materials, without many of
the fossils of the inferior beds becoming mixed up with the overlying
crag, so that considerable difficulty must be occasionally experienced
by the palaeontologist in deciding which species belong severally to each
group. The red crag being formed in a shallower sea, often resembles in
structure a shifting sand bank, its layers being inclined diagonally,
and the planes of stratification being sometimes directed in the same
quarry to the four cardinal points of the compass, as at Butley. That
in this and many other localities, such a structure is not deceptive or
due to any subsequent concretionary re-arrangement of particles, or to
mere lines of colour, is proved by each bed being made up of flat pieces
of shell which lie parallel to the planes of the smaller strata.
Some fossils, which are very abundant in the red crag, have never been
found in the white or coralline division; as, for example, the _Fusus
contrarius_ (fig. 144.), and several species of _Buccinum_ (or _Nassa_)
and _Murex_ (see figs. 145, 146.), which two genera seem wanting in
the lower crag.
[4 Illustrations: Fossils characteristic of the Red Crag.
Fig. 144. _Fusus contrarius._
Fig. 145. _Murex alveolatus._
Fig. 146. _Nassa granulata._
Fig. 147. _Cypraea coccinelloides._
Fig. 144. half nat. size; the others nat. size.]
Among the bones and teeth of fishes are those of large sharks
(_Carcharias_), and a gigantic skate of the extinct genus _Myliobates_, and
many other forms, some common to our seas, and many foreign to them.
The distinctness of the fossils of the coralline crag arises in part from
higher antiquity, and, in some degree, from a difference in the
geographical conditions of the submarine bottom. The prolific growth of
corals, echini, and a prodigious variety of testacea, implies a region of
deeper and more tranquil water; whereas, the red crag may have formed
afterwards on the same spot, when the water was shallower. In the mean time
the climate may have become somewhat cooler, and some of the zoophytes
which flourished in the first period may have disappeared, so that the
fauna of the red crag acquired a character somewhat more nearly resembling
that of our northern seas, as is implied by the large development of
certain sections of the genera _Fusus_, _Buccinum_, _Purpura_, and
_Trochus_, proper to higher latitudes, and which are wanting or feebly
represented in the inferior crag.
Some of the corals of the lower crag of Suffolk belong to genera unknown in
the living creation, and of a very peculiar structure; as, for example,
that represented in the annexed fig. (148.), which is one of several
species having a globular form. The great number and variety of these
zoophytes probably indicate an equable climate, free from intense cold in
winter. On the other hand, that the heat was never excessive is confirmed
by the prevalence of northern forms among the testacea, such as the
_Glycimeris_, _Cyprina_, and _Astarte_. Of the genus last mentioned (see
fig. 149.) there are about fourteen species, many of them being rich in
individuals; and there is an absence of genera peculiar to hot climates,
such as _Conus_, _Oliva_, _Mitra_, _Fasciolaria_, _Crassatella_, and
others. The cowries (_Cypraea_, fig. 147.), also, are small, and belong to a
section (_Trivia_) now inhabiting the colder regions. A large volute,
called _Voluta Lamberti_ (fig. 150.), may seem an exception; but it differs
in form from the volutes of the torrid zone, and may, like the living
_Voluta Magellanica_, have been fitted for an extra-tropical climate.
[Illustration: Fig. 148. _Fascicularia aurantium_, Milne Edwards. Family,
_Tubuliporidae_, of same author.
Coral of extinct genus, from the inferior or coralline crag, Suffolk.
_a._ exterior.
_b._ vertical section of interior.
_c._ portion of exterior magnified.
_d._ portion of interior magnified, showing that it is made up of long,
thin, straight tubes, united in conical bundles.]
[Illustration: Fig. 149. _Astarte_ (_Crassina_, Lam.); species common to
upper and lower crag.
_Astarte Omalii_, Lajonkaire; Syn. _A. bipartita_, Sow. Min. Con. T.
521. f. 3.; a very variable species most characteristic of the
coralline crag, Suffolk.]
[Illustration: Fig. 150. _Voluta Lamberti_, young individ.]
The occurrence of a species of _Lingula_ at Sutton is worthy of remark,
as these _Brachiopoda_ seem now confined to more equatorial latitudes,
and the same may be said still more decidedly of a species of _Pyrula_,
allied to _P. reticulata_. Whether, therefore, we may incline to the
belief that the mean annual temperature was higher or lower than now,
we may at least infer that the climate and geographical conditions were
by no means the same at the period of the Suffolk crag as those now
prevailing in the same region.
Of the echinoderms of the coralline crag about eleven species are known,
but some of these are in too fragmentary a condition to admit of exact
comparison. Of six which are the most perfect, Prof. E. Forbes has been
able to identify three with recent species: one of which, of the genus
_Echinus_, is British; a second, _Echinocyamus_, British and Mediterranean;
and a third, _Echinus monilis_, a Mediterranean species, also found fossil
in the faluns of Touraine.
One of the most interesting conclusions deduced from a careful comparison
of the shells of these British Older Pliocene strata and those now
inhabiting our seas, has been pointed out by Prof. E. Forbes. It appears
that, during the glacial period, a period intermediate, as we have seen,
between that of the crag and our own times, many shells, previously
established in the temperate zone, retreated southwards to avoid an
uncongenial climate. The Professor has given a list of fifty shells which
inhabited the British seas while the coralline and red crag were forming,
and which are wanting in the Pleistocene or glacial deposits. They must,
therefore, after their migration to the south, have made their way
northwards again. In corroboration of these views, it is stated that all
these fifty species occur fossil in the Newer Pliocene strata of Sicily,
Southern Italy, and the Grecian Archipelago, where they may have enjoyed,
during the era of floating icebergs, a climate resembling that now
prevailing in higher European latitudes.[166-A]
In the red crag at Felixstow, in Suffolk, Professor Henslow has found the
ear-bones of no less than four species of cetacea, which, according to Mr.
Owen, are the remains of true whales of the family _Balaenidae_. Mr. Wood is
of opinion that these cetacea may be of the age of the red crag, or if not
that they may be derived from the destruction of beds of coralline crag. I
agree with him that the supposition of their having been washed out of the
London clay, in which no _Balaenidae_ have yet been met with, is improbable.
Strata containing fossil shells, like those of the Suffolk crag, above
described, have been found at Antwerp, and on the banks of the Scheldt
below that city. In 1840 I observed a small patch of them near Valognes, in
Normandy; and there is also a deposit containing similar fossils at St.
George Bohon, and several places a few leagues to the S. of Carentan, in
Normandy; but they have never been traced farther southwards.
_Subapennine strata._--The Apennines, it is well known, are composed
chiefly of secondary rocks, forming a chain which branches off from the
Ligurian Alps and passes down the middle of the Italian peninsula. At the
foot of these mountains, on the side both of the Adriatic and the
Mediterranean, are found a series of tertiary strata, which form, for the
most part, a line of low hills occupying the space between the older chain
and the sea. Brocchi, as we have seen (p. 105.), was the first Italian
geologist who described this newer group in detail, giving it the name of
the Subapennines; and he classed all the tertiary strata of Italy, from
Piedmont to Calabria, as parts of the same system. Certain mineral
characters, he observed, were common to the whole; for the strata consist
generally of light brown or blue marl, covered by yellow calcareous sand
and gravel. There are also, he added, some species of fossil shells which
are found in these deposits throughout the whole of Italy.
We have now, however, satisfactory evidence that the Subapennine beds of
Brocchi belong, at least, to three periods. To the Miocene we can refer a
portion of the strata of Piedmont, those of the hill of the Superga, for
example; to the Older Pliocene, part of the strata of northern Italy, of
Tuscany, and of Rome; while the tufaceous formations of Naples, of Ischia,
and the calcareous strata of Otranto, are referable to the Newer Pliocene,
and in great part to the Post-Pliocene period.
That there is a considerable correspondence in the mineral composition of
these different Italian groups is undeniable; but not that exact
resemblance which should lead us to assume a precise identity of age,
unless the fossil remains agreed very closely. It is now indispensable that
a new scrutiny should be made in each particular district, of the fossils
derived from the upper and lower beds--especially such localities as Asti
and Parma, where the formation attains a great thickness; and at Sienna,
where the shells of the incumbent yellow sand are generally believed to
approach much more nearly, as a whole, to the recent fauna of the
Mediterranean than those in the subjacent blue marl.
The greyish brown or blue marl of the Subapennine formation is very
aluminous, and usually contains much calcareous matter and scales of mica.
Near Parma it attains a thickness of 2000 feet, and is charged throughout
with marine shells, some of which lived in deep, others in shallow water,
while a few belong to freshwater genera, and must have been washed in by
rivers. Among these last I have seen the common _Limnea palustris_ in the
blue marl, filled with small marine shells. The wood and leaves, which
occasionally form beds of lignite in the same deposit, may have been
carried into the sea by similar causes. The shells, in general, are soft
when first taken from the marl, but they become hard when dried. The
superficial enamel is often well preserved, and many shells retain their
pearly lustre, part of their external colour, and even the ligament which
unites the valves. No shells are more usually perfect than the microscopic
foraminifera, which abound near Sienna, where more than a thousand
full-grown individuals may be sometimes poured out of the interior of a
single univalve of moderate dimensions.
The other member of the Subapennine group, the yellow sand and
conglomerate, constitutes, in most places, a border formation near the
junction of the tertiary and secondary rocks. In some cases, as near the
town of Sienna, we see sand and calcareous gravel resting immediately on
the Apennine limestone, without the intervention of any blue marl.
Alternations are there seen of beds containing fluviatile shells, with
others filled exclusively with marine species; and I observed oysters
attached to many limestone pebbles. This appears to have been a point
where a river, flowing from the Apennines, entered the sea when the
tertiary strata were formed.
The sand passes in some districts into a calcareous sandstone, as at San
Vignone. Its general superposition to the marl, even in parts of Italy and
Sicily where the date of its origin is very distinct, may be explained if
we consider that it may represent the deltas of rivers and torrents, which
gained upon the bed of the sea where blue marl had previously been
deposited. The latter, being composed of the finer and more transportable
mud, would be conveyed to a distance, and first occupy the bottom, over
which sand and pebbles would afterwards be spread, in proportion as rivers
pushed their deltas farther outwards. In some large tracts of yellow sand
it is impossible to detect a single fossil, while in other places they
occur in profusion. Occasionally the shells are silicified, as at San
Vitale, near Parma, from whence I saw two individuals of recent species,
one freshwater and the other marine (_Limnea palustris_, and _Cytherea
concentrica_, Lam.), both perfectly converted into flint.
_Rome._--The seven hills of Rome are composed partly of marine tertiary
strata, those of Monte Mario, for example, of the Older Pliocene period,
and partly of superimposed volcanic tuff, on the top of which are usually
cappings of a fluviatile and lacustrine deposit. Thus, on Mount Aventine,
the Vatican, and the Capitol, we find beds of calcareous tufa with
incrusted reeds, and recent terrestrial shells, at the height of about 200
feet above the alluvial plain of the Tiber. The tusk of the mammoth has
been procured from this formation, but the shells appear to be all of
living species, and must have been embedded when the summit of the Capitol
was a marsh, and constituted one of the lowest hollows of the country as it
then existed. It is not without interest that we thus discover the
extremely recent date of a geological event which preceded an historical
era so remote as the building of Rome.
MIOCENE FORMATIONS.
_Faluns of Touraine._--The Miocene strata, corresponding with those named
by many geologists "Middle Tertiary," will next claim our attention. Near
the towns of Dinan and Rennes, in Brittany, and again in the provinces
bordering the Loire, a tertiary formation, containing another assemblage of
fossils, is met with, to which the name of _Faluns_ has been long given by
the French agriculturists, who spread the shelly sand and marl over the
land, in the same manner as the crag was formerly much used in Suffolk.
Isolated masses of these faluns occur from near the mouth of the Loire,
near Nantes, as far as a district south of Tours. They are also found at
Pontlevoy, on the Cher, about 70 miles above the junction of that river
with the Loire, and 30 miles S.E. of Tours. I have visited all the
localities above mentioned, and found the beds to consist principally of
sand and marl, in which are shells and corals, some entire, some rolled,
and others in minute fragments. In certain districts, as at Doue, in the
department of Maine and Loire, 10 miles S.W. of Saumur, they form a soft
building-stone, chiefly composed of an aggregate of broken shells, corals,
and echinoderms, united by a calcareous cement; the whole mass being very
like the coralline crag near Aldborough and Sudbourn in Suffolk. The
scattered patches of faluns are of slight thickness, rarely exceeding 50
feet; and between the district called Sologne and the sea they repose on a
great variety of older rocks; being seen to rest successively upon gneiss,
clay-slate, and various secondary formations, including the chalk; and,
lastly, upon the upper freshwater limestone of the Parisian tertiary
series, which, as before mentioned (p. 106.), stretches continuously from
the basin of the Seine to that of the Loire.
At some points, as at Louans, south of Tours, the shells are stained of a
ferruginous colour, not unlike that of the red crag of Suffolk. The species
are, for the most part, marine, but a few of them belong to land and
fluviatile genera. Among the former, _Helix turonensis_ (fig. 45. p. 30.)
is the most abundant. Remains of terrestrial quadrupeds are here and there
intermixed, belonging to the genera Deinotherium, Mastodon, Rhinoceros,
Hippopotamus, Chaeropotamus, Dichobune, Deer, and others, and these are
accompanied by cetacea, such as the Lamantine, Morse, Sea-calf, and
Dolphin, all of extinct species.
Professor E. Forbes, after studying the fossil testacea which I obtained
from these beds; informs me that he has no doubt they were formed partly on
the shore itself at the level of low water, and partly at very moderate
depths, not exceeding 10 fathoms below that level. The molluscous fauna of
the "faluns" is on the whole much more littoral than that of the red and
coralline crag of Suffolk, and implies a shallower sea. It is, moreover,
contrasted with the Suffolk crag by the indications it affords of an
extra-European climate. Thus it contains seven species of _Cypraea_, some
larger than any existing cowry of the Mediterranean, several species of
_Oliva_, _Ancillaria_, _Mitra_, _Terebra_, _Pyrula_, _Fasciolaria_, and
_Conus_. Of the cones there are no less than eight species, some very
large, whereas the only European cone is of diminutive size. The genus
_Nerita_, and many others, are also represented by individuals of a type
now characteristic of equatorial seas, and wholly unlike any Mediterranean
forms. These proofs of a more elevated temperature seem to imply the higher
antiquity of the faluns as compared with the Suffolk crag, and are in
perfect accordance with the fact of the smaller proportion of testacea of
recent species found in the faluns.
Out of 290 species of shells, collected by myself, in 1840, at
Pontlevoy, Louans, Bossee, and other villages 20 miles south of Tours;
and at Savigne, about 15 miles north-west of that place; 72 only could
be identified with recent species, which is in the proportion of 25 per
cent. A large number of the 290 species are common to all the
localities, those peculiar to each not being more numerous than we might
expect to find in different bays of the same sea.
The total number of mollusca from the faluns, in my possession, is 302,
of which 45 only were found by Mr. Wood to be common to the Suffolk
crag. The number of corals obtained by me at Doue, and other localities
before adverted to, amounts to 43, as determined by Mr. Lonsdale, of
which 7 agree specifically with those of the Suffolk crag. Only one has,
as yet, been identified with a living species. But it is difficult, if
not impossible, to institute at present a satisfactory comparison
between fossil and recent _Polyparia_, from the deficiency of our
knowledge of the living species. Some of the genera occurring fossil in
Touraine, as the _Astrea_, _Lunulites_, and _Dendrophyllia_, have not
been found in European seas north of the Mediterranean; nevertheless the
_Polyparia_ of the faluns do not seem to indicate on the whole so warm a
climate as would be inferred from the shells.
It was stated that, on comparing about 300 species of Touraine shells
with about 450 from the Suffolk crag, 45 only were found to be common to
both, which is in the proportion of only 15 per cent. The same small
amount of agreement is found in the corals also. I formerly endeavoured
to reconcile this marked difference in species with the supposed
co-existence of the two faunas, by imagining them to have severally
belonged to distinct zoological provinces or two seas, the one opening
to the north, and the other to the south, with a barrier of land between
them, like the Isthmus of Suez, separating the Red Sea and the
Mediterranean. But I now abandon that idea for several reasons;
among others, because I succeeded in 1841 in tracing the Crag fauna
southwards in Normandy to within 70 miles of the Falunian type, near
Dinan, yet found that both assemblages of fossils retained their
distinctive characters, showing no signs of any blending of species
or transition of climate.
On a comparison of 280 Mediterranean shells with 600 British species, made
for me by an experienced conchologist in 1841, 160 were found to be common
to both collections, which is in the proportion of 57 per cent., a fourfold
greater specific resemblance than between the seas of the crag and the
faluns, notwithstanding the greater geographical distance between England
and the Mediterranean than between Suffolk and the Loire. The principal
grounds, however, for referring the English crag to the older Pliocene and
the French faluns to the Miocene epochs, consist in the predominance of
fossil shells in the British strata identifiable with species, not only
still living, but which are now inhabitants of neighbouring seas, while the
accompanying extinct species are of genera such as characterize Europe. In
the faluns, on the contrary, the recent species are in a decided minority,
and many of them, like the associated extinct testacea, are much less
European in character, and point to the prevalence of a warmer climate,--in
other words, to a state of things receding farther from the present
condition of Europe, geographically and climatologically, and doubtless,
therefore, receding farther in time.
_Bordeaux._--A great extent of country between the Pyrenees and the Gironde
is overspread by tertiary deposits, which have been more particularly
studied in the environs of Bordeaux and Dax, from whence about 700 species
of shells have been obtained. A large proportion of these shells belong to
the same zoological type as those of Touraine; but many are peculiar, and
the whole may possibly constitute a somewhat older division of the Miocene
period than the faluns of the Loire. We must wait, however, for farther
investigations, in order to decide this question with accuracy.
_Piedmont._--Many of the shells peculiar to the hill of the Superga, near
Turin, agree with those found at Bordeaux and Dax; but the proportion of
recent species is much less. The strata of the Superga consist of a bright
green sand and marl, and a conglomerate with pebbles, chiefly of green
serpentine, and are inclined at an angle of more than 70 deg.. This formation,
which attains a great thickness in the valley of the Bormida, is probably
one of the oldest Miocene groups hitherto discovered.
_Molasse of Switzerland._--If we cross the Alps, and pass from Piedmont
to Savoy, we find there, at the northern base of the great chain, and
throughout the lower country of Switzerland, a soft green sandstone much
resembling some of the beds of the basin of the Bormida, above
described, and associated in a similar manner with marls and
conglomerate. This formation is called in Switzerland "molasse," said to
be derived from "mol," "_soft_" because the stone is easily cut in the
quarry. It is of vast thickness, and probably divisible into several
formations. How large a portion of these belong to the Miocene period
cannot yet be determined, as fossil shells are often entirely wanting.
In some places a decided agreement of the fossil fishes of the molasse
and faluns has been observed. Among those common to both, M. Agassiz
pointed out to me _Lamna contortidens_, _Myliobates Studeri_, _Spherodus
cinctus_, _Notidanus primigenius_, and others.
_Lisbon._--Marine tertiary strata near Lisbon contain shells which agree
very closely with those of Bordeaux, and are therefore referred to the
Miocene era. Thus, out of 112 species collected by Mr. Smith of Jordanhill,
between 60 and 70 were found to be common to the strata of Bordeaux and
Dax, the recent species being in the proportion of 21 per cent.
_Older Pliocene and Miocene formations in the United States._--Between the
Alleghany mountains, formed of older rocks, and the Atlantic, there
intervenes, in the United States, a low region occupied principally by beds
of marl, clay, and sand, consisting of the cretaceous and tertiary
formations, and chiefly of the latter. The general elevation of this plain
bordering the Atlantic does not exceed 100 feet, although it is sometimes
several hundred feet high. Its width in the middle and southern states is
very commonly from 100 to 150 miles. It consists, in the South, as in
Georgia, Alabama, and South Carolina, almost exclusively of Eocene
deposits; but in North Carolina, Maryland, Virginia, and Delaware, more
modern strata predominate, which I have assimilated in age to the English
crag and Faluns of Touraine.[172-A] If, chronologically speaking, they can
be truly said to be the representatives of these two European formations,
they may range in age from the Older Pliocene to the Miocene epoch,
according to the classification of European strata adopted in this chapter.
The proportion of fossil shells agreeing with recent, out of 147 species
collected by me, amounted to about 17 per cent., or one-sixth of the
whole; but as the fossils so assimilated were almost always the same as
species now living in the neighbouring Atlantic, the number may
hereafter be augmented, when the recent fauna of that ocean is better
known. In different localities, also, the proportion of recent
species varied considerably.
[Illustration: Fig. 151. _Fulgur canaliculatus._ Maryland.]
[Illustration: Fig. 152. _Fusus quadricostatus_, Say. Maryland.]
On the banks of the James River, in Virginia, about 20 miles below
Richmond, in a cliff about 30 feet high, I observed yellow and white sands
overlying an Eocene marl, just as the yellow sands of the crag lie on the
blue London clay in Suffolk and Essex in England. In the Virginian sands,
we find a profusion of an Astarte (_A. undulata_, Conrad), which resembles
closely, and may possibly be a variety of, one of the commonest fossils of
the Suffolk crag (_A. bipartita_); the other shells also, of the genera
_Natica_, _Fissurella_, _Artemis_, _Lucina_, _Chama_, _Pectunculus_, and
_Pecten_, are analogous to shells both of the English crag and French
faluns, although the species are almost all distinct. Out of 147 of these
American fossils I could only find 13 species common to Europe, and these
occur partly in the Suffolk crag, and partly in the faluns of Touraine; but
it is an important characteristic of the American group, that it not only
contains many peculiar extinct forms, such as _Fusus quadricostatus_, Say
(see fig. 152.), and _Venus tridacnoides_, abundant in these same
formations, but also some shells which, like _Fulgur carica_ of Say, and
_F. canaliculatus_ (see fig. 151.), _Calyptraea costata_, _Venus
mercenaria_, Lam., _Modiola glandula_, Totten, and _Pecten magellanicus_,
Lam., are recent species, yet of forms now confined to the western side of
the Atlantic, a fact implying that the beginning of the present
geographical distribution of mollusca dates back to a period as remote as
that of the Miocene strata.
Of ten species of zoophytes which I procured on the banks of the James
River, two were identical with species of the Faluns of Touraine. With
respect to climate, Mr. Lonsdale regards these corals as indicating a
temperature exceeding that of the Mediterranean, and the shells would
lead to similar conclusions. Those occurring on the James River are in
the 37th degree of N. latitude, while the French faluns are in the 47th;
yet the forms of the American fossils would scarcely imply so warm a
climate as must have prevailed in France, when the Miocene strata
of Touraine originated.
Among the remains of fish in these Post-Eocene strata of the United
States are several large teeth of the shark family, not distinguishable
specifically from fossils of the faluns of Touraine, and the
Maltese tertiaries.
_India._--The freshwater deposits of the Sub-Himalayan or Sewalik Hills,
described by Dr. Falconer and Captain Cautley, may perhaps be regarded as
Miocene. Like the faluns of Touraine, they contain the Deinotherium and
Mastodon. Whether any of the associated freshwater and land shells are of
recent species is not yet determined. The occurrence in them of a fossil
giraffe and hippopotamus, genera now only living in Africa, as well as of a
camel, implies a geographical state of things very different from that now
established in the same parts of India. The huge Sivatherium of the same
era appears to have been a ruminating quadruped bigger than the rhinoceros,
and provided with a large upper lip, or probably a short proboscis, and
having two pair of horns, resembling those of antelopes. Several species of
monkey belonged to the same fauna; and among the reptiles, several
crocodiles, larger than any now living, and an enormous tortoise, _Testudo
Atlas_, the curved shell of which measured 20 feet across.
FOOTNOTES:
[162-A] See paper by E. Charlesworth, Esq.; London and Ed. Phil. Mag. No.
xxxviii. p. 81., Aug. 1835.
[162-B] See Monograph on the Crag Mollusca. Searles Wood, Paleont.
Soc. 1848.
[163-A] In regarding the Suffolk crag, both red and coralline, as
older Pliocene instead of Miocene, I am only returning to the
classification adopted by me in the Principles and Elements of
Geology up to the year 1838.
[166-A] E. Forbes, Mem. Geol. Survey, Gt. Brit., vol. i. 386.
[172-A] Proceedings of the Geol. Soc. vol. iv. part 3. 1845, p. 547.