!! I ivn UKS ON EVOLUTION 



in 



imagine any two groups more definitely and dis- 

 tly separated, notwithstanding certain charac- 

 tm which they possess in common. 



As we trace the history of birds back in time, we 

 tint I their remains, sometimes in great abundance, 

 throughout the whole extent of the tertiary rocks ; 

 but, so far as our present knowledge goes, the birds 

 of the tertiary rocks re tain the same essential char- 

 acters as the birds of the present day. In other 

 words, the tertiary birds come within the definition 

 ( t' the class constituted by existing birds, and are as 

 much separated from reptiles as existing birds are. 

 Not very long ago no remains of birds had been 

 found below the tertiary rocks, and I am not sure 

 but that some persons were prepared to demonstrate 

 t hat they could not have existed at an earlier period. 

 But, in the course of the last few years, such remains 

 have been discovered in England ; though, unfortu- 

 nately, in so imperfect and fragmentary a condition, 

 tliat it is impossible to say whether they differed 

 from existing birds in any essential character or not. 

 In your country the development of the cretaceous 

 series of rocks is enormous ; the conditions under 

 which the later cretaceous strata have been de- 

 <1 ,-uv highly favourable to the preservation nt' 

 organic remains; and the researches, full of labour 

 .nid ri>k, which have been carried on by Profo 

 M.'irsh in these cretaceous rueks !' Western 

 America, h;m- rewarded him with the discovery of 

 .-thirds >f which we had hitherto no concep- 



