1 8 INTRODUCTION. 



day can justify us in believing that these widely separated de- 

 posits are strictly " contemporaneous," in the sense that they 

 were deposited at exactly the same period of time. We should 

 have to believe, if this conclusion is to be justified, that in Silu- 

 rian times the ocean spread over a much larger area of the 

 earth's surface than it does now, and that its temperature and 

 depth were unnaturally uniform : and there are, perhaps, some 

 who would accept this view. What has been said about the Silu- 

 rian Rocks as a whole applies with still greater force to certain 

 of the minor subdivisions of the same, which contain many of 

 exactly the same specific forms in parts of the globe very 

 widely removed from one another. It is the very identity of 

 the fossils, however, which proves that the beds in question, 

 from their geographical position, cannot have been deposited 

 at exactly the same time, though they doubtless belong to the 

 same period, and may even be said to be related to one an- 

 other, as far as the identical fossils are concerned, by lineal 

 descent. Similar remarks might be made about the Devonian, 

 Permian, Triassic, Jurassic, Cretaceous, and other formations ; 

 but it is not necessary further to multiply examples. 



If we consider the present state of things upon the globe, we 

 shall be further convinced of the justice of these views, which 

 were first prominently brought forward by Professor Huxley. 

 If we could suddenly remove the sea from the earth, we should 

 find at various points of the earth's surface deposits of different 

 kinds, now concealed from us by the ocean, or only partially 

 known by dredgings or soundings. Thus, we should find vast 

 accumulations of calcareous matter, in the form of coral-rock 

 and coral-reef, where now rolls the Pacific Ocean. In high 

 northern and low southern latitudes we should find great de- 

 posits of sand and mud, with angular blocks of stone, the 

 whole derived from the ice-clad regions of the poles. Over 

 vast areas, again, in the deep Atlantic, we should find an im- 

 palpable chalky mud, or "ooze." All these different deposits 

 are obviously and necessarily " contemporaneous," not only in 

 the geological acceptation of the word, but in its most literal 

 sense. In spite of this fact they would not contain the same 

 fossils ; and, indeed, they would be characterised by organic 

 remains which would be wholly different in each case. The 

 coral-reefs of the Pacific would be essentially characterised by 

 the abundance of the remains of reef-building corals, though 

 they would also present other tropical forms of life, especially 

 Brachiopods and Echinoderms. The glacial mud of the Polar 

 regions would contain the remains of Arctic molluscs, along 

 with such other animals as delight in severe cold. Lastly, the 



