NO. 4 CAMBRIAN' AND PRE-CAMBRIAN AT HELENA 273 



CAMBRIAN SECTION OF THE LITTLE BELT MOUNTAINS 

 Dr. Walter H. Weed has published a description of the Cambrian 

 rocks of the Little Belt Mountains section 60 to 70 miles east of 

 Helena and 30 to 40 miles east of the Big Belt Mountains.' The 

 several formations were here first *named as follows: 



7. Yogo limestone 130 feet. 



6. Dry Creek shale 40 



5. Pilgrim limestone 97 " 



4. Park shale 800 " 



3. Meagher limestone loo-j- " 



2. Wolsey shale 150 " 



1. Flathead sandstone 160 " 



Unconformity. 

 Belt series : Spokane shale. 



A brief description is given of each formation and a plate (pi. 40) 

 of comparative colmnnar sections of Middle Cambrian formations in 

 central Montana. 



Algonkian formations. — The pre-Cambrian formations exposed on 

 Belt Creek south of Neihart are described and the statement made 

 tha the unconformity between the upper formation, the Spokane 

 sha'e, and the Cambrian Flathead sandstone is well shown on Saw- 

 mil' Creek.^ 



"'lie Belt formations are named as follows : 



5. Spokane shale 210 feet. 



4. Grayson shale 955 " 



3. Newland limestone 567 " 



2. Chamberlin shale 2,078 " 



I. Neihart quartzite 702 " 



Unconformity. 



Archean. 



STRATIGRAPHIC SECTION OF PALEOZOIC FORMATIONS IN THE 

 BIG SNOWY MOUNTAINS, MONTANA' 



In an unpublished manuscript report by W. R. Calvert of the U. S. 

 Geological Survey, on the Big Snowy Mountains area 60 miles east of 

 the Little Belt Mountains, based on work done by him and his party 

 during the field seasons of 1907 and 191 1, there is a brief account of 

 ■the Cambrian and pre-Cambrian formations in the vicinity of Half 



^Twentieth Ann. Rept., U. S. Geol. Surv., Pt. 3, 1900, pp. 284-287. 

 - Idem, p. 283. 



^ Published by permission of the Director of the U. S. Geological Survey. 

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