270 THE ORIGIN OF THE OLDEST FOSSILS, ETC. 



eight are Crustacea, fifty-one are trilobites, and trails and burrows 

 show the existence of at least six species of bottom forms, pro- 

 bably worms or Crustacea. The most notable characteristic of 

 this fauna is the completeness with which these few species outline 

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

 the simple unspecialised 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 fossiHferous beds of the lower Cambrian rest upon beds 

 which 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 favourable for the preservation 

 and the discovery of fossils. Modern discovery has brought the 

 difficulty which 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 and comparative embryology and the study 

 of the habits and affinities of organisms tell us of times more 

 ancient than the oldest fossils, and give a more perfect record of 

 the early history of Hfe than palaeontology. 



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 

 occurrence of several periods when modification was comparatively 

 rapid. 



We are living in a period of intellectual progress, and, among 

 terrestrial 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 one hundred 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. Mea- 

 sured in years, the middle tertiary is very remote, but it is very 

 modern compared with the whole history of the fossiUferous rocks. 



