THE OlIIGIN OF THE OLDEST FOSSILS AKD THE DISCOV- 

 ERY OF THE BOTTOM OF THE OCEAN.i 



By W. K. Brooks, 



I'rofessor of Zoolot/i) in ihe Johns Hopkins University. 



In the Origin of Species Darwin says that the sudden appearance of 

 si)ecies belonging to several of the main divisions of the animal king- 

 dom in the lowest known fossiliferous rocks is at present inexplicable 

 and may be truly iirged as a valid objection to his views. 



It 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 for- 

 midable objection ; for it seems doubtful whether the earth, in a tit state 

 for the habitation of living creatures, has lasted long enough. To the 

 question why we do not iind such Ibssiliferous deposits belonging to 

 these assumed earliest periods i)rior to the Cambrian system I can give 

 no satistiictory answer." 



On its geological side this dihiculty 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 tyi)es have modern representatives. The ])aleontological 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 one hundred and forty-one American species from the 

 Lower Cambrian is distributed over most of the marine groups of the 

 animal kingdom, and except for tlu; absence of the remains of verte- 

 brated animals, the whole ])rovince of animal life is almost as com- 

 pletely covered by these one hundred and forty-one 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 gas- 



^From the Jourual of Geology; July-August, 1894; Vol. 11, No. 5. 



359 



