SUMMARIES OF CURRENT NORTH AMERICAN PRE- 

 CAMBRIAN LITERATURE. 



{Continued from p. 425, Vol. VII.) 



Walcott 1 discusses pre-Cambrian fossiliferous formations of North 

 America. In two cases only have fossils of undoubted organic origin 

 been shown to occur in formations of reasonably certain pre-Cambrian 

 age, namely, the Grand Canyon of Arizona, and the Belt terrane of 

 Montana. The Etcheminian terrane of New Brunswick and Newfound- 

 land is doubtfully a third instance. 



A brief account is given of the stratigraphy, of each of the areas of 

 pre-Cambrian sedimentary rocks. No new points appear except in 

 the description of the Belt terrane of Montana ; the account of the 

 Belt terrane is therefore the only one summarized with reference to 

 stratigraphy. 



The Belt terrane of Montana covers an area of more than 6000 

 square miles in central Montana. The principal beds of the terrane 

 are as follows : 



Marsh shales ------- 300 feet. 



Helena limestone ------ 2,400 " 



Empire shales ------- 600 " 



Spokane shales ------ 1,500 " 



Greyson shales ------- 3,000 " 



Newland limestone - 2,000 " 



Chamberlin shales ------ 1,500 " 



Neihart quartzite and sandstone - 700 " 



12,000 feet. 

 Throughout the area the Belt terrane is overlain unconformably by 

 middle Cambrian rocks (Flathead). The Cambrian rocks rest on vari- 

 ous members of the Belt series, and in places the Belt terrane is entirely 

 wanting, the Cambrian resting directly on the Archean schists. In 

 such cases, moreover, the character of the Belt beds indicates that the 

 Cambrian overlaps the Belt series. The base of the Cambrian is not 

 markedly conglomeratic. At most of the outcrops where the lower 



1 Pre-Cambrian Fossiliferous Formations, by Charles D. Walcott : Bull. Geol. 

 Soc. Am., Vol. X, 1899, pp. 199-244. 



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