360 THE O'RIGIN OF THE OLDEST FOSSILS. 



teropods, fifteen are pteropods, eight are Crustacea, fifty-one are trilo- 

 bites, and trails and burrows show the existence of at least six species 

 of bottom forms, probably worms or Crustacea. The most notable char- 

 acteristic of this fauna is the completeness with which these few sj^ecies 

 outline the whole fauna, of the modern sea floor. Far from showing us 

 the simi)le unspecialized ancestors of modern animals, they are most 

 intensely modern themselves in the zoological sense, and they belong- 

 to the same order of nature as that which prevails at the present day. 



The fossiliferous beds of the Lower Cambrian rest upon beds Avhich 

 are miles in vertical thickness, and are identical in all their physical 

 features with those which contain this fauna. They prove beyond 

 question that the waters in which they were laid down were as fit for 

 supporting life at the beginning as at the end of the enormous lapse of 

 time which they represent, and that all the conditions have since been 

 equally favorable for the preservation and the discovery of ibssils. 

 Modern discovery has brouglit the difiiculty Avhich Darwin points out 

 into clearer view, but geologists are no more prepared than he was to 

 give a satisfactory solution, although I shall now try to show that the 

 study of living animals in their relations to the world around them 

 does help us, and that comparative anatomy aud conq)arative embry- 

 ology and the study of the habits aud affinities of organisms tell ns of 

 times more ancient than the oldest fossils and give a more jierfect 

 record of the early history of life than paleontology. 



While the history of life as told by fossils has been slow and 

 gradual, it has not been uniform, for we have evidence of the occur- 

 rence of several periods when modification was comparatively rapid. 



We are living in a period of iutellectual progress, and among terres- 

 trial animals cunning now counts for more than size or strength, and 

 fossils show that, while the average size of mammals has diminished 

 since the Middle Tertiary, the size of their brains has increased more 

 than 100 per cent; that the brain of a modern mammal is more than 

 twice as large, compared with its body, as the brain of its ancestors in 

 the Middle Tertiary. Measured in years the Middle Tertiary is very 

 remote, but it is very modern compared with the whole history of the 

 fossilifenms rocks, although more of brain development has been 

 effected in this short time than in all preceding time from the beginning. 



The later paleozoic and early secondary fossils mark another i)eriod 

 of rapid change, when the fitness of the land for animal life, and the 

 presence of land plants, brought about the evolution of terrestrial 

 animals. 



I shall give reasons for seeing, in the Lower Cambrian, another period 

 of rapid change, when a new factor — the discovery of the bottom of the 

 ocean — began to act in the modification of species, and I shall try to 

 show that, while animal life was abundant long before, the evolution of 

 animals likely to be preserved as fossils took place with comparative 

 rapidity, and that the zoological features of the Lower Cambrian are of 



