568 STUDIES FOR STUDENTS 



But as carbonate deposits are characteristic of the open sea, so 

 are sihcious, feldspathic, and argillaceous deposits dominant upon 

 the land surface, and thus a separate argument is derived for the 

 view that in pre-Cambrian times the continents possessed at least 

 their present extension, an argument, however, which requires 

 further testing in regard to the premises as to the poverty of lime- 

 stones. 



It would seem, therefore, that the 12,000 feet of the Belt terrane, 

 consisting, as it does, of from 37 to 50 per cent, of dolomitic lime- 

 stones is far from being an occurrence holding an unusual proportion 

 of continental deposits and that the conclusion derived from its 

 study in regard to their presence in important quantity is therefore 

 susceptible of wider application. 



