ioo Selections from Huxley 



by the Pacific has been deepened thousands of feet, since 

 the present inhabitants of that sea came into existence. 



Thus there is not a shadow of a reason for believing 

 that the physical changes .of the globe, in past times, 

 5 have been effected by other than natural causes. 



Is there any more reason for believing that the con- 

 comitant modifications in the forms of the living inhabi- 

 tants of the globe have been brought about in other ways? 

 Before attempting to answer this question, let us try 



10 to form a distinct mental picture of what has happened, 

 in some special case. 



The crocodiles are animals which, as a group, have a 

 very vast antiquity. They abounded ages before the 

 chalk was deposited ; they throng the rivers in warm 



15 climates, at the present day. There is a difference in 

 the form of the joints of the backbone, and in some 

 minor particulars, between the crocodiles of the present 

 epoch and those which lived before the chalk; but, in 

 the cretaceous epoch, as I have already mentioned, the 



20 crocodiles had assumed the modern type of structure. 

 Notwithstanding this, the crocodiles of the chalk are not 

 identically the same as those which lived in the times 

 called "older tertiary," which succeeded the cretaceous 

 epoch; and the crocodiles of the older tertiaries are not 



25 identical with those of the newer tertiaries, nor are these 

 identical with existing forms. I leave open the question 

 whether particular species may have lived on from epoch 

 to epoch. But each epoch has had its peculiar crocodiles; 

 though all, since the chalk, have belonged to the modern 



30 type, and differ simply in their proportions, and in such 

 structural particulars as are discernible only to trained 

 eyes. 



How is the existence of this long succession of dif- 

 ferent species of crocodiles to be accounted for? 



