150 



DEVELOPMENT OF OKGANIC LIFE 



[Ch. IX. 



C* 



classes and orders of the living vegetable creation are ful] y 

 represented. The variety and completeness of the fossil flor* 

 then attained continued to be conspicuous throughout a Ion 



)rms 

 mor< 



and specifically, to those now in being. On the whole there 

 appears therefore to have been an advance in the fossil flora in 

 the course of ages, although the cryptogamous plants of the 

 primary periods may some of them have been more perfect or 

 of a higher grade than any of the same class now living. The 



Gymnogens (cycads and conifers) 



more 



abundant, 



as also the Monocotyledons in the Secondary epochs, while 

 in the Tertiary periods all the leading forms of the most 

 complex dicotyledons now inhabiting the globe appear to 

 have flourished. 



Fossil Animals. — We may next turn to the animal kingdom, 

 and consider the arguments derived from fossil vertebrata and 

 invertebrata in favour of progressive development. When- 

 ever these arguments are founded on negative evidence, we 

 cannot be too cautious in our reasoning, and we must always 

 bear in mind that it has been evidently no part of the plan of 

 Nature to hand down to us a complete or systematic record of 

 the former history of the animate world. We may have failed 

 to discover a single shell, marine or freshwater, or a single 

 coral or bone in shale or sandstone, even in such a formation as 

 that of the valley of the Connecticut, in which the footprints 

 of bipeds and quadrupeds abound ; but such failure may have 

 arisen, not because the population of the land or sea was scanty 

 at that era, but because in general the preservation of any 

 relics of the animals or plants of former times is the excep- 

 tion to a general rule. Time so enormous as that contemplated 



ni' 



to constitute the rule, and so impose on the imagination as to 

 lead us to infer the non-existence of creatures of which no 

 monuments happen to remain. The late Edward Forbes re- 

 marked, that few geologists are aware how large a proportion 

 of all known species of fossils are founded on single specimens, 

 while a still greater number are founded on a few individuals 

 discovered in one spot. This holds true not only in regard to 







ai 



to 



a. 



