52 INTRODUCTION. 



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 deposits 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 impalpable chalky mud, or " ooze." All these dif- 

 ferent 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 ooze of the deep Atlantic would contain innumer- 

 able Foraminifera, along with siliceous Sponges and Crinoids. We 

 learn, therefore, from this, that contemporaneous deposits not only 

 do not necessarily contain the same fossils, but that, if widely sep- 

 arated geographically, they may be characterised by wholly dissimilar 

 assemblages of organisms. 



It may happen, again, as pointed out by Sir Charles Lyell, that 

 deposits belonging to different geographical and zoological provinces 

 may, as regards space, be nearly approximated, and, as regards time, 

 may be actually contemporaneous, and yet may not contain any fos- 

 sils in common, or only a very few. If, for example, any sudden 

 upheaval were to lay bare what is now the floor of the Red Sea, to- 

 gether with that of the Mediterranean, we should find the two areas 

 to contain deposits actually synchronous as regards the time of their 

 deposition, and very near to one another in point of distance, and 

 yet containing, upon the whole, entirely distinct groups of organic 

 remains. We learn, therefore, from this, that owing to the exist- 

 ence of geographical barriers, it is possible for contemporaneous 

 deposits to be found in close contiguity, in a single region, and yet 

 to contain very different fossils. 



Again, it has been abundantly proved that even within the limits 

 of a single ocean deposits are now in process of formation which, 

 though strictly contemporaneous in point of time, nevertheless differ 

 from one another altogether both in mineral characters and in their 

 included organic remains. Thus, the mechanical deposits formed 



