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Zbc ©rigin of the ©l&eet 3fo6eil6 an^ tbe 

 Discoveri? of tbe :S5ottom of tbe ©cean,* 



By W. K. Brooks. 



IN the Origin of Species^ Darwin says that the sudden appear- 

 ance of species belonging to several of the main divisions 

 of the animal kingdom in the lowest known fossiliferous 

 rocks is at present inexplicable, and may be truly urged as a valid 

 objection to his views. 



If his theory be true, he says that "it is indisputable that before 

 the lowest Cambrian stratum was deposited long periods elapsed, 

 as long as, or probably far longer than the whole interval from the 

 Cambrian age to the present day ; and that during these vast 

 periods the world swarmed with living creatures. Here," he 

 says, "we encounter a formidable objection; for it seems doubtful 

 whether the earth, in a fit state for the habitation of living crea- 

 tures, has lasted long enough." "To the question why we do 

 not find such fossiliferous deposits belonging to these assumed 

 earliest periods prior to the Cambrian system I can give no satis- 

 factory answer." 



On its geological side this difficulty is even greater than it was 

 in Darwin's day, for we now know that the fauna of the lower 

 Cambrian was rich and varied ; that most of the modern types of 

 animal life were represented in the oldest fauna which has been 

 discovered, and that all its types have modern representatives. 

 The palaeontological side of the subject has been ably summed up 

 by Walcott in an interesting memoir on the oldest fauna which is 

 known to us from fossils, and his collection 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 bottom 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, 



* A paper read before the University Scientific Association, and printed 

 in the Journal of Geology^ Chicago, 1894. 



