456 THE JOURNAL OF GEOLOGY. 



of 141 American species from the lower Cambrian is distributed 

 over most of the marine groups of the animal kingdom, and 

 except for the absence of the remains of vertebrated animals, 

 the whole province of animal life is almost as completely covered 

 by these 141 species as it could be by a collection from the bot- 

 tom of the modern ocean. Four of the American species are 

 sponges, two are hydrozoa, nine are actinozoa, twenty-nine are 

 brachiopods, three are lamellibranchs, thirteen are gasteropods, 

 fifteen are pteropods, eight are Crustacea, fifty-one are trilobites, 

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

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

 ble 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 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 

 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 favorable 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 compara- 

 tive 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 life 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 



