352 THE CAUSES OF THE xi 



composition. The jaw would thus be deposited 

 immediately, while the rest of the body would 

 float and drift away altogether, ultimately reaching 

 the sea, and perhaps becoming destroyed. The 

 jaw becomes covered up and preserved in the river 

 silt, and thus it comes that we have such a 

 curious circumstance as that of the lower jaws in 

 the Stonesfield slates. So that, you see, faulty as 

 these layers of stone in the earth's crust are, 

 defective as they necessarily are as a record, the 

 account of contemporaneous vital phenomena 

 presented by them is, by the necessity of the case, 

 infinitely more defective and fragmentary. 



It was necessary that I should put all this very 

 strongly before you, because, otherwise, you might 

 have been led to think differently of the com- 

 pleteness of our knowledge by the next facts I 

 shall state to you. 



The researches of the last three-quarters of a 

 century have, in truth, revealed a wonderful 

 richness of organic life in those rocks. Certainly 

 not fewer than thirty or forty thousand different 

 species of fossils have been discovered. You have 

 no more ground for doubting that these creatures 

 really lived and died at or near the places in 

 which we find them than you have for like 

 scepticism about a shell on the sea-shore. The 

 evidence is as good in the one case as in the other. 



Our next business is to look at the general 

 character of these fossil remains, and it is a subject 



