NO. lO DISCOVERIES OF CAMBRIAN BEDS — RESSER 5 



cline, but the recent discoveries indicate the possible presence of at 

 least Middle Cambrian, as well as the previously known younger 

 Paleozoics. 



RECENT DISCOVERIES OF CAMBRIAN BEDS IN THE 

 ROCKY MOUNTAINS 



It will be easier to understand the true significance of the following 

 finds if we take them up in the order of their discovery, which also 

 automatically places them in their proper provincial grouping. 



Pcnd Oreille Lake. — The first discovery extending the area of 

 known Cambrian outcrops into the supposed gap across the Beltian 

 area was made about 1920 by Dr. Edward Sampson, at that time a 

 member of the United States Geological Survey. He found a good 

 Camljrian section along the southern shores of Pend Oreille Lake in 

 northern Idaho. Here limestones and shales contain abundant Middle 

 Cambrian fossils, which recall both those of the Ovando region in 

 central Montana and also others in the Canadian Rockies, thus show- 

 ing that Cambrian seaways extended across the western as well as 

 the eastern portions of the supposedly barren Beltian area, where 

 Walcott's studies in 1905 had shown the existence of Cambrian. 



Extension of the Ovando area. — During recent years the Montana 

 State geologists have been studying the sedimentary beds of north- 

 western Montana, particularly with the view to unraveling the com- 

 plicated Beltian sedimentary record. This work greatly extended the 

 Cambrian, both geographically and stratigraphically, in the Ovando 

 region about the head of Sun River observed by Walcott in 1905. 

 Study of these data is now under way by Dr. C. F. Deiss of the State 

 University at Missoula, Mont. 



South Kootenay Pass. — The third significant discovery was made 

 by Dr. G. S. Hume, of the Canadian Geological Survey, during the 

 field season of 1932, when he collected what appear to be Middle 

 Cambrian fossils north of Red Deer River, in the vicinity of North 

 Kootenay Pass, southern Alberta. Here shales, with layers and lenses 

 of limestone, overlie about 100 feet of quartzites, which in turn rest 

 on the Beltian with an erosional unconformity between. The Middle 

 Cambrian is said to be overlain by Silurian strata in the southernmost 

 locality found, but a little farther north is directly succeeded by 

 Devonian. The Cambrian, as well as the other mentioned Paleozoic 

 beds, vary rather rapidly in thickness. This discovery reduces the 

 gap, as previously outlined, by many miles in a north-south direction, 

 as the Pend Oreille find did in the east-west direction. 



