2 C. D. WALCOTT ALGONKIAN FORMATIONS OP MONTANA 



Page 



Correlation of Montanian with Canadian sections 21 



Source of sediments 26 



Summary 27 



Introduction 



In 1898 I made a reconnaissance of the pre-Cambrian formations of 

 the Belt mountains of Montana and published the results.* The section 

 extended from the unconformable Cambrian above to Archean complex 

 at the base. In 1900 I crossed the Belt mountains and endeavored to 

 trace the connection, north of Helena, of the Belt terrane and the pre- 

 Cambrian rocks of the Rocky Mountain "front" at Lewis and Clark pass 

 and north on the south fork of the Dearborn river. It was evident that 

 a great series of strata extended westward beneath the Cambrian that was 

 in general similar to the Belt terrane, but quite different in detail. In 

 1901, at my request, Mr Bailey Willis studied the Front ranges of the 

 Kocky mountains in northern Montana and found a great series of strata 

 referred to the Algonkian.f In the survey of the Cceur d'Alene mining 

 district of Idaho Mr F. L. Eansome, assisted by Mr F. C. Calkins, found 

 most of the region underlain by stratified, siliceous rocks, referred to the 

 Algonkian.J During the field season of 1905 Mr Calkins continued the 

 study of the Algonkian rocks of Idaho, and extended his examinations 

 into western Montana, nearly to Iiavalli, on the Northern Pacific railroad. 

 I also had the opportunity of studying the pre-Cambrian rocks of north- 

 western Montana in 1905, and of measuring the section from northwest 

 of Scapegoat mountain on the Continental divide, westward, crossing the 

 Swan and Mission ranges, to the canyon of Jocko creek above Ravalli. 



In this paper I wish to compare the various sections thus far studied 

 and to correlate them as far as practicable. The Camp Creek, Mission 

 Range section will be taken as the type section, owing to its being capped 

 by Cambrian strata and being of greater vertical range than any other 

 known section. It embraces portions of the northern section of Mr 

 Willis and the western section in the Cceur d'Alene district. 



Strattgraphic Sections 

 camp creek, mission range section 



The section in general. — The upper portion of Scapegoat mountain, in 

 the southeastern portion of the Lewis and Clark forest reserve, is formed 



* Bull. Geol. Soc. Am., vol. 10, pp. 201-215, 235-239. 



t Bull. Geol. Soc. Am., vol. 13, pp. 314-324. 



1 Manuscript of Geologic Folio, U. S. Geological Survey. 



