A Manual of Elementary Geology

es of animals and plants have lived at successive periods - Distinct provinces of indigenous species - Great extent of single provinces - Similar laws prevailed at successive geological periods -

classes of rocks, and I shall now treat of the aqueous rocks in particular, or of the

and, thirdly, organic remains. Some aid can occasionally be derived from a fourth kind of proof, namely, the fact of one deposit including

s at the bottom the most ancient. So, of a series of sedimentary formations, they are like volumes of history, in which each writer has recorded the annals of his own times, and then laid down the book, with the last written page uppermost, upon the volume in wh

st can rarely be deceived by these exceptional cases. When he finds that the strata are fractured, curved, inclined, or vertical, he knows that the original order of superposition must be doubtful, and he then endeavours to find sections in some neighbou

diment over wide areas at one period, but at successive periods have been charged, in the same region, with very different kinds of matter. The first observers were so astonished at the vast spaces over which they were able to follow the same homogeneous rocks in a horizontal direction, that they came hastily to the opinion, that the whole globe had been environed by a succession of distinct aqueous formations, disposed round the nucleus of the planet, like the concentric coats of an onion. But although, in fact, some formations may be continuous over districts as large as half of Europe, or even more, yet most of them either terminate wholly within narrower lim

formation, or of the contemporaneous origin of two deposits in distant place

ons, if we examine strata in the direction of their

and has led to a conviction, that at successive periods of the past, the same area of land and water has been inhabited by species of animals and plants even more distinct than those which now people the antipodes, or which now co-exist in the arctic, temperate, and tropical zones. It appears, that from the remotest periods there has be

e poi ruppe la

im, and then

ue as chronological tests, giving to each of them, in the eyes of the g

g in each position so perfect an identity of mineral aspect as to be undistinguishable. Such exact repetitions, however, of the same mixtures of sediment have not often been produced, at distant periods, in precis

of living beings, we find that the habitable surface of the sea and land may be divided into a considerable number of distinct provinces, each peopled by a peculiar assemblage of animals and plants. In the Principles of Geology, I have endeavoured to point o

istinct fossils will be imbedded in contemporaneous deposits. If it were otherwise-if the same species abounded in every climate, or in every part of the globe where, so far as we can discover, a corresponding tem

geological researches have proved that the same laws prevailed at remote periods; for the fossils are often identical t

cea and zoophytes may be very local, and each region has probably some species peculiar to it, still a considerable number are common to the whole Mediterranean. If, therefore, at some future period, the bed of this inlan

o, where another class of rocks is now forming; where showers of volcanic ashes occasionally fall into the sea, and streams of lava overflow its bottom; and where, in the intervals between volcanic eruptions, beds of sand and clay are frequently derived from the waste of cliffs, or the turbid waters of rivers. Limestones, moreover, such as the Italian travertins, are here and there precipitated from the

joining parts of the Mediterranean, although the two seas are separated only by the narrow isthmus of Suez. Of the bivalve shells, according to Philippi, not more than a fifth are common to the Red Sea and the sea around Sicily, while the proportion of univalves (or Gasteropoda) is still smaller, not exceeding eighteen in a hundred. Calcareous formations have accumulated on a great scale in the Red Sea in modern times, and fossil shells of existing species

and-floods, and those winds which drift clouds of sand along the deserts, might carry down into the Red Sea the same shells of fluviatile and land testacea which the Nile is sweeping into its delta, together with some remains of ter

of terrestrial species of distinct zoological and botanical provinces will be proved by the identity of the marine beings which inhabited the intervening space. Thus, for example, the land quadruped

ng particular formations of remote periods, has sometimes been able to trace the gradation from one ancient province to another, by observing carefully the fossils of all the intermediate places. His success in thus acquiring a knowledge of the zoological or botanical geography of very distant eras has been mainly owing to this circumstance, that the mineral character has no tendency to be affected by climate. A large river

d if so, pal?ontological characters will be of more importance in geological classification than mineral composition; but it is idle to discuss the relative valu

o formations from want of clear sections exhibiting their true order of position, or because the strata of each group are vertical. In such cases we sometimes discover that the more modern rock has been in part derived from the degradation of the older. Thus, for example, we may find in one part of a country chalk wit

ding to the views of classification which different geologists entertain; but when we have adopted a certain system of arrangeme

. 1

groups, instead of as many strata. It will then be seen that in the middle all the superimposed formations are present; but in

. 1

of Bristol.

n 4 miles. a, b.

erior

L

red san

sian con

al me

iferous l

red san

formations 5 and 6. Here at the southern end of the line of section we meet with the beds No. 3. (the New Red Sandstone) resting immediately on No. 6., while farther north, as at Dundry Hill, we behold six groups superimposed one upon the other, comprising all the strata

arises, not from the destruction of what once existed, but because no strata of an intermediate age were ever deposited on the inferior rock. They were not

the other. He must then trace these formations, by attention to their mineral character and fossils, continuously, as far as possible, from the starting point. As often as he me

n of strata throughout a great part of Europe, and have adopted pretty generally the f

anged in what is termed a descending Series, or beginning with

luding those of the R

cene. Tertiary, Supracretaceo

er Pli

Mio

Eoc

ondary, or Me

reen

Wea

per O

ddle O

ower

Li

Tr

ry fossiliferous,

Co

sandstone,

per Si

wer Si

nd older fossi

oups comprise monuments relating to equal portions of past time, or of the earth's history. But we can assert that they each relate to successive periods, during which certain anim

s less numerous than those in the above table, and more nearly co-ordinate in value than the sections called prima

ble from all classes of fossils, not even those most generally distributed, such as shells, corals, and fish, such generaliza

of Western Europe div

ary } from the Post-Plioce

Maestricht Chalk to the L

the Wealden to t

Keuper, Muschelkalk, and Bun

cluding Magnesian Limestone (Zechstein), Coa

the Upper Silurian to the olde