RELATIONS BETWEEN CAMBRIAN AND BELT TERRANE 



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range, but a few miles distant from the former exposures, the Belt terrane 

 is entirely wanting, and the Cambrian rests directly on the Archean 

 schists, as it does at Neihart. The character of the Belt beds indicates, 

 moreover, that the Cambrian overlaps 

 the Belt shoreline. Forty miles south- 

 east of Neihart, in the Deep Creek and 

 Greyson Creek sections, on the south- 

 western slope of the Big Belt moun- 

 tains, the Flathead rests on the Spokane 

 shales, but at a higher horizon than at 

 the head of Sawmill canyon. Twenty- 

 two miles north - northeast of Deep 

 creek, in Whites can^'on, the full thick- 

 ness of the Greyson shale and also about 

 1,000 feet of the Helena limestone occur 

 beneath the Cambrian sandstones. 



Crossing the valley of the Missouri 

 river from Whites canyon directl}'' west- 

 ward 10 miles to the SjDokane hills, on 

 the west side of the river, one finds a 

 syncline of Cambrian resting directly 

 on the red Spokane shales. Continu- 

 ing westward on the same line to the 

 city of Helena, a distance of 14 miles, 

 the Cambrian sandstones are found rest- 

 ing on shales 250 feet above the Helena 

 limestone, or fully 3,000 feet above the 

 contact horizon in the Spokane hills. 

 Following the line of contact to the 

 southeast for 1 mile, the Cambrian sand- 

 stones may be seen resting directly on 

 the massive beds of the Helena lime- 

 stone, a slight unconformity occurring 

 at the point of contact, as shown by 

 figure 3. A mile farther southeast there 

 are 6 feet of shale above the limestone, 

 a slight unconformity being shown be- 

 tween it and the Cambrian. The sec- 

 tion east from Helena extends down- 

 ward through some 2,000 feet or more of 

 limestone and interbedded shales and 

 several hundred feet of silicious, green- 



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