286 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



\OL. 64 



character of the Belt beds indicates, moreover, that the Cambrian overlaps 

 the Belt (Period) shoreline. Forty miles southeast of Neihart, in the Deep 

 Creek and Grayson Creek sections, on the southwestern slope of the Big Belt 

 Mountains, 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 Canyon, the full thickness of the Grayson shale and 

 also about 1,000 feet of the (Algonkian) Helena limestone occur beneath the 

 Cambrian sandstones. 



', r 'J .'', 



LZI 



CAMB/f/y4 /V 

 SANDSTONE 



HELfNA 

 L/MESrO/ve 



Fig. 12. — Unconformity between 

 Helena Limestone and Cambrian Flat- 

 head Sandstone. The locality indicated 

 is 1.25 miles southeast of the suburb of 

 Lenox, and 2 miles southeast of the Capi- 

 tol building at Helena. Montana. 



Crossing the valley of the Missouri River from Whites Canyon directly 

 westward 10 miles to the Spokane Hills, on the west side of the river, one 

 finds a syncline of Cambrian resting directly on the red Spokane shales. 

 Continuing westward on the same line to the city of Helena, a distance of 14 

 miles, the Cambrian sandstones are found resting on shales 250 feet above 



CAMBRIAN 

 SAf^DSTONE 



HELENA 

 UMESTONE 



Fig. 13. — Unconformity between 

 Marsh Shale and Cambrian Flathead 

 Sandstone. The locality indicated is 

 about I mile southeast of the locality 

 of fig. 12, or 3 miles southeast of the 

 Capitol building. 



the Helena limestone, or fully 3,000 feet above the contact horizon in the 

 Spokane Hills. Following the line of (the Flathead-quartzite-Spokane shale) 

 contact to the southeast for i mile, the Cambrian sandstones may be seen 

 resting directly on the massive beds of the Helena limestone, a slight uncon- 

 formity occurring at the point of contact, as shown by figure 12. A mile 

 farther southeast there are 6 feet of shale above the limestone, a slight uncon- 

 formity being shown between it and the Cambrian (fig. 13). The section east 

 from Helena extends downward through some 2,000 feet or more of limestone 

 and interbedded shales and several hundred feet of siliceous, greenish shales 



