THE PROTEROZOIC ERA. 217 



fossils, and if this hypothesis is applicable to any extensive formation 

 of limestone, it may be applicable to those of the Proterozoic systems. 

 But even without reliance on the limestone, the fossils leave no doubt 

 of the existence of life in the Proterozoic era. 



The best-preserved fossils are those of eurypterus-like Crustacea. 

 There are also tracks of two genera of annelids, and other undeter- 

 mined forms. Besides these certain fossils, there are obscure forms 

 which appear to be referable to brachiopods and pteropods. It is 

 significant that the oldest definite fossils yet found are well-developed 

 Crustacea, forms well up in the animal kingdom. 



Climate. 



Since inferences concerning the climate of any period are drawn 

 chiefly from fossils, and since fossils are exceedingly rare in the Protero- 

 zoic strata, there is little warrant for any conclusion concerning the cli- 

 mate of the period. Certain pre-Cambrian conglomerates of Ontario, 

 shown in the Cobalt region and elsewhere, have been interpreted re- 

 cently, as of glacial origin, tut the evidence thus far presented does 

 not seem to be conclusive on this point. 



1 Coleman, Geol. Soc. Am., 1906. 



