OF ORGANIC NATURE. 51 



like of now only in tropical regions. If I went below 

 that, I should come upon the chalk, and there I should 

 find something altogether different, the remains ot 

 ichthyosauri and pterodactyles, and ammonites, and 

 so forth. 



I do not know what Mr. Godwin Austin would say 

 comes next, but probably rocks containing more am- 

 monites, and more ichthyosauri and plesiosauri, with 

 a vast number of other things ; and under that I should 

 meet with yet older rocks, containing numbers of strange 

 shells and fishes ; and in thus passing from the surface 

 to the lowest depths of the earth's crust, the forms of 

 animal life and vegetable life which I should meet with 

 in the successive beds would, looking at them broadly, 

 be the more different the further that I went down. 

 Or, in other words, inasmuch as we started with the 

 clear principle, that in a series of naturally-disposed 

 mud beds the lowest are the oldest, we should come 

 to this result, that the further we go back in time the 

 more difference exists between the animal and vege- 

 table life of an epoch and that which now exists. That 

 was the conclusion to which I wished to bring you at 

 the end of this Lecture. 



