﻿part 1] 



ANNIVERSARY ADDRESS OF THE PRESIDENT. 



Ixv 



The Use or the Higher Verteprates in Stratigraphical 



The study of fossil fishes, to which I referred last year, seems 

 to show that each of the successive dominant groups is sharply 

 distinguished from its immediate predecessor by some fundamental 

 character marking an advance towards the extreme adaptation 

 for locomotion in water, which was ultimately attained in the 

 Cretaceous Period. It is also evident that various members of each 

 of these successive groups soon became specialized for every 

 possible mode of life in the circumstances of the time. Fishes 

 of the same general outward appearance and habit have thus 

 originated repeatedly from progressively higher groups ; similar 

 adaptations have recurred with only minor differences ; and nearly 

 the same changes, though perhaps with increasing intensity, have 

 always marked the approach to racial old age. These phenomena 

 are, indeed, so remarkable, that the question arises as to whether 

 animals of apparently the same family, genus, or species mav 

 not originate more than once from separate series of ancestors. 

 We may even hesitate further in deciding whether or no the 

 really fundamental advances in life at successive periods have 

 occurred more than once in the faunas of which they are respec- 

 tively characteristic. 



The study of fishes, however, is scarcely sufficient to solve these 

 problems, because the large majority of the fossils are marine, the 

 animals would spread rapidly and widely, and the limits of the 

 seas in which they lived are never clearly recognizable. The 

 higher vertebrates, which inhabited the land, seem to be a much 

 more hopeful source of necessary facts ; for the land has always 

 been subdivided into well-defined areas^ isolated by seas, mountains, 

 and deserts. Animals in these several areas must often have deve- 

 loped independently for long periods ; alterations in the barriers 

 can be detected by the geologist when he studies the migrations 

 and mingling of faunas ; while, as researches progress, the varying 

 geography of successive periods may be more or less successfully 

 restored. Like the fishes, the terrestrial vertebrates have advanced 

 by successive fundamental steps towards perfection in powei's of 

 locomotion, and during this progress have at each stage diverged 

 into various analogous specializations. They have, indeed, advanced 

 one step farther by the final increase in the relative size and 



VOL. lxxii. e 



GrEOLOGY. 



