A Manual of Elementary Geology

in determining the chronology of tertiary formations - Increasing proportion of living species of shells in strata of newer origin - Terms Eocene, Miocene, and Pliocene - Pos

ables given at the end of the last chapter, it will be necessary to say som

ums of Europe; and it was long before their real extent and thickness, and the various ages to which they belong, were fully recognized. They were observed to occur in patches, some of freshwater, others of marine origin, their geographical area being usually small a

of marine, others of freshwater origin, lying one upon the other. The fossil shells and corals were perceived to be almost all of unknown species, and to have in general a near affinity to those now inhabiting warmer seas. The bones and skeletons of land

nferred by Mr. T. Webster to be of the same age as those of Paris, because the greater number of the fossil shells were specifically identical. For the sa

ar Paris and London. An attempt was therefore made at first to refer the whole to one period; and when at length this seemed impracticable, it was contended that as in the Parisian series there were many subordinate formations of considerable thickness w

ss of classification. A more scrupulous attention to specific distinctions, aided by a careful regard to the relative position of the strata containing them, led at

ly termed "Crag" in Suffolk, lay decidedly over a deposit which was the continuation of the blue clay of London. At the same time he remarked that the fossil testacea in thes

te with shells which form a low range of hills, flanking the Apennines on both sides, from the plains of the Po to Calabria. These l

idence of superposition was brought to bear in support of this opinion; for other strata, contemporaneous with those of Bordeaux, were observed in one district (the Valley of the Loire), to overlie the Parisian formation, and in another (in Piedmont) to underlie the Subapennine beds. The first example of these was pointed out in 1829 by M. Desnoyers, who ascertained that the sand and marl of marine origin called Faluns, near Tours, in the basin of the Loire, full of se

respects of an intermediate character. For this new type it becomes necessary to institute the new genus B., in which are included all species afterwards brought to light, which agree more nearly with B. than with the types of A. or C. In like manner a new formation is met with in geology, and the characters of its fossil fauna and flora investigated. From that moment it is considered as a record of a certain period of the earth's history, and a standard to which other deposits may be compared. If any are found containing the same or nearly the same organic remains, and occupying the same relative position, they are regarded

ial nature of their divisions becomes more apparent, in proportion to the increased number of objects brought to light. But in separating families and genera, they have no other alternative than to avail themselves of such breaks as still remain, or of every hiatus in the chain of animated beings which is not yet filled up. So in geology, we may be eventually compelled to resort to sections o

erence is found in the four groups of testacea now living in the Baltic, English Channel, Black Sea, and Mediterranean, although all these seas have many species in common. In like manner a considerable diversity in the fossils of different tertiary formations, which have been thrown down in distinct seas, estuaries, bays, and lakes, does not always imply a distinctness in the times when they were produced, but may have arisen from climate and conditions of physical geography wholly independent of time. On the other hand, it is now abundantly clear, as the result of geological investigation, that different sets of tertiary strata, immediately superimposed upon each other, contain distinct imbedded species of fossils, in

d volcanic tuff of the country round Naples, and of the contiguous island of Ischia. Another deposit has been found at Uddevalla, in Sweden, in which the shells do not agree with those found near Naples. But although in these three cases there may be sca

than three-fourths of the shells agree with species still living, while the remainder are extinct. Hence we may conclude that all these, greatly diversified as are their organic remains, belong to one and the same era, or to a period immediately antecedent to the Post-Pliocene, because there has been time in each of the areas alluded to for an equal or nearly equal amount of change

mer alterations in the animate world, or the continual going out and coming in of species, has been every where exactly equal in equal quantities of time. The form of the land and sea, and the climate, may have changed more in one region than in another; and consequently there may have been a more rapid destruction and renova

fined to a limited space, or to one geographical province of animals or plants, but affects several other surrounding and contiguous provinces. In each of these, moreover, analogous alterations of the stations and habitations of species are simultaneously in progress, reacting in the manner already alluded to on the first province. Hence, long before the geography of any particular district can be essentially altered, the flora and fauna throughout the world will have been materially modified by countless disturbances in the mutual relation of the various members of the organic creation to each other. To assume that in one large area inhabited exclusively by a single assemblage of species any important revolution in

on respecting the affinity or discordance of the organic beings of the two epochs compared; and the same may be said if we have plants and vertebrated animals in one series and only shells in another. Although corals are more abundant, in a fossil state, than plants, reptiles, or fish, they are still rare when contrasted with shells, especially in the European tertiary formations. The utility of the testacea is, moreover, enhanced by the circumstance that some forms are proper to the sea, others to the land, and others to freshwater. Rivers scarcely ever fail to carry

the former, the great duration of species in this class, for they appear to have surpassed in longevity the greater number of the mammalia and fish. Had each species inhabited a very limited space, it could never, when imbedded in strata, have enabled

upper; the lower comprising the oldest formations of Paris and London before-mentioned; th

rm, lists of all the shells known to him to occur both in some tertiary formation and in a living state, for the express purpose of ascertaining the proportional number of fossil species identical with the recent which characterized successive groups; and this table, planned by us in common, was published by me in 1833.[110-A] The number of tertiary fossil shells examined by M. Deshayes was about 3000; and the recent species with which they had been compared about 5000. The result then arrived at was, that in the lower tertiary strata, or those of London and Paris, there were about 31/2 per cent. of species identical with recent; in the middle tertiary of the Loire and Gironde about 17 per cent.; and in the upper tertiary or Subapennine beds, from 35 to 50 per cent. In formations still more modern, some of which I had part

πλειον, pleion, more, and καινο?, cainos, recent) a comparative plurality of the same. It may assist the memory of students to remind them, that the Miocene contain a m

nd Older Pliocene deposits often contain the remains of mammalia, reptiles, and fish, exclusively of extinct species. But the reader must bear in mind that the te

which the results before mentioned were obta

the Pliocene period

Mioce

Eocen

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0

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pecies have also been added to our collections in great abundance; and at the same time a more copious supply of individuals both of fossil and recent species, some of which were previously very rare, have been procured,

ocene Fo

characterized by having all the imbedded fossil shells identical with species now living, whereas even the Newer Pliocene

d thickness, in which no signs of man or his works can be detected. In some of these, of a date long anterior to the times of history and tradition, the bones of extinct quadrupeds have been

osits accumulated at the bottom of lakes and seas within the last 4000 or 5000 years can neither be insignificant in volume or extent. They lie hidden, for the most part, from our sight; but we have opportunities of examining them at certain points where newly-gained land in the deltas of rivers has been cut through during floods, or wh

l periods, it is found that rocks containing shells, all, or nearly all, of which still inhabit the neighbouring sea, may be traced for some distance into the interior, and often to a considerable elevation above the level of the sea. Thus, in the country round Naples, the post-pliocene strata, consisting of clay and horizontal beds of volcanic tuff, rise at certain points to the height of 1500 feet. Although the marine shells are exclusively of living species, they are not accompanied like those on the coast at Puzzuoli by any

prodigious thickness, interstratified in some parts with marl, and here and there with great beds of solid lava. Visconti ascertained by trigonometrical measurement that this mountain was 2605 feet above the level of the sea. Not far from its summit, at the height of about 2000 feet, as also near Moropano, a villag

that only one, Pecten medius, now living in the Red Sea, was absent from the Mediterranean. Notwithstanding this, he adds, "the condition of the sea when the tufaceous beds were deposited must have been considerably different from its present state; for Tellina striata was then common, and is now rare; Lucina spinosa was both more abundant and grew to a larger size; Lucina fragilis,

pe, where it may equal 5 feet in a century. If we could assume that there had been an average rise of 21/2 feet in each hundred years for the last fifty centuries, this would give an elevation of 125 feet in that period. In other words, it would follow that the shores, and a considerable area of the former bed of the Baltic and North Sea, had been uplifted vertically to that amount, and converted into land in the course of the last 5000 years. Accordingly, we find near Stockholm, in Sweden, horizontal beds of sand, loam, and marl containing the same peculiar assemblage of testacea which now live in the brackish waters of

ascend to the height of 200 feet; and beds of clay and sand of the same age attain elevations of 300 and even 700 feet in Norway, where they have been usually described as "raised beaches." They are, however, th

uralist of Norway), the species do not constitute such an assemblage as now inhabits corresponding latitudes in the German Ocean. On the contrary, they decidedly represent a more arctic fauna.[114-A] In orde

ce is here brought to light. On the other hand, we have every reason for inferring on independent grounds (namely, the rate of upheaval of land in modern times) that the antiquity of the deposits in question must be very great. For if we assume, as before suggested, that the mean rate of continuous ver

human period. Recent strata have been traced along the coasts of Peru and Chili, inclosing shells in abundance, all agreeing specifically with those now swarming in the Pacific. In one bed of this kind, in the island of San Lorenzo, near Lima, Mr. Darwin found, at the altitude of 85 feet above the sea, pieces of cotton-thread, plaited rush, and the head of a stalk of Indian corn, the whole of which had evidently been imbedded with the shells. At the s

ells, of species now living in the adjacent ocean. With them are included arrow-heads, fragments of pottery, and other articles of human workmanship. A limestone with similar contents has been formed, and is still forming, in St. Domingo. But there are also more anc

continuing to be terrestrial or freshwater in character. This appears to have happened in the deltas both of the Po and Ganges, for recent artesian borings, penetrating to the depth of 400 feet, have there shown that fluviatile strata, with shells of recent species, together with ancient surfaces of land supporting turf and forests, are depressed hundreds of feet below the sea level.[116-A] Should these countries be once more slowly upraised, the rivers would carve out valleys through the horizontal and unconsolidated strata as they rose, sweeping away the greater portion of them, and leaving mere fragments in the shape of terraces skirting newly-formed alluvial plains, as monuments of the former levels at which the rivers ran. Of this nature are "the bluffs,"

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f the Mi

lluv

Loe

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reta

as yet incomplete-we may still approximate to a minimum of the time which such an operation must have taken, by ascertaining experimentally the annual discharge of water by the Mississippi, and the mean annual amount of solid matter contained in its waters. The lowest estimate of the time required would lead us to assign a high antiquity, amounting to many tens of thousands of years to the existing delta, the origin of which is ne

, rarely exceeding the size of a man's head. Its entire thickness amounts, in some places, to between 200 and 300 feet; yet there are often no signs of stratification in the mass, except here and there at the bottom, where there is occasionally a slight intermixture of drifted materials derived from subjacent rocks. Unsolidified as it is, and of so perishable a nature, that every streamlet flowing over it cuts out for itself a deep gully, it usually terminates in a vertical cliff, from the surface of which land shells are seen here and there to project in relief. In all these features it presents a precise counterpart to the loess of the Mississippi. It is so homogeneous as generally to exhibit no signs of stratification, owing, probably, to its materials having been derived fr

sses of it appear at the foot of the Vosges on the left bank, and at the base of the mountains of the Black Forest on the right bank. The Kaiserstuhl, a volcanic mountain which stands in the middle of the plain of the Rhine near Freiburg, has been covered almost everywhere with this loam, as have the extinct volcanos between Coblentz and Bonn. Near Andernach, in the Kirchweg, the loess containing the usual shells alternates wi

modern aspect; and it has filled up in part the crater of the Roderberg, an extinct volcano near Bonn. In 1833 a well

sign a very modern date to these eruptions. This curious point, therefore, deserves to be reconsidered; since it may possibly have happened that the waters of the Rhine, swollen by the melting of snow and ice, and flowing at a great height through a valley choked up with loess, may have swept away

en. The barrier of the lake might be placed somewhere in the narrow and picturesque gorge of the Rhine between Bingen and Bonn. But this theory fails altogether to explain the phenomena; when we discover that that gorge itself has once been filled with loess, which must have been tranquilly deposited in it, as also in the lateral valley of the Lahn, communicating with t

upposed lake from the ocean would require to be, at least, as high as the mountains called the Siebengebirge, near Bonn, the loftiest summit of which, the Oehlberg, is 1209 feet abo

red, the general fall of the waters between the Alps and the ocean was lessened; and both the main and lateral valleys, becoming more subject to river inundations, were partially filled up with fluviatile silt, containing land and freshwater shells. When a thickness of many hundred feet of loess had been thrown down slowly by this operation, the whole region was once more upheaved gradually. During this upward movement most of the fine loam would be carried off by the denuding power of rains and rivers; and thus the original valleys might have

lowings of rivers above supposed would favour the multiplication of amphibious mollusks, such as the Succinea (fig. 107.), which is almost everywhere characteristic of this formation, and is sometimes accompanied, as near Bonn, by another species, S. amphibia (fig. 34. p. 29.). Among other abundant fossils are Helix plebeium and Pupa muscorum. (See Figur

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ea elo

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mus

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pleb

e, I found the vertebr? of fish, together with the usual shells. These vertebr?, according to M. Agassiz, belong decidedly to the Shark family, perhaps to the genus Lamna. In explanation of their occurr

recent shells of the genera Planorbis, Lymnea, Paludina, &c., from 50 to 80 feet thick, with a bed of loess much resembling that of the Rhine, occasionally incumbent on them. In these modern limestones used for building, the bones of Elephas primigenius, Rhinoceros tichorinus, Ursus spel?us, Hy?na spel?a, with the horse, ox, deer, and othe

eptilian remains which have been

ery modern period the filling up and re-excavation of the valleys; an operation which doubtless co