728 L. D. BURLING CAMBRO-ORDOVICIAN Js'^EAR MOUNT ROBSON 



The Devonian has been fomid to lie disconformably on the Cambrian or 

 early Ordovician rocks in Eoche Miette, west of Jasper, Alberta;^ in 

 ISTorth Kootenay Pass, south of Crowsnest Pass, between British Colum- 

 bia and Alberta;^ near Elko, west of Fernie, British Columbia;^ on 

 Beaver Creek, northeast of Helena, Montana ;^° in the Sawback Range 

 west of Banff, Alberta ; in the mountains at the east end of Lake Minne- 

 wanka, north of Banff, Alberta; in the moimtains at the head of Upper 

 Columbia Lake, south of Golden, British Columbia, and elsewhere. 



A survey of these various occurrences leads to the following conception 

 of the relations. In the Canadian Pacific Eailway section it appears that 

 where the L^pper Cambrian is thick and characterized by what we might 

 call the accepted type of Upper Cambrian fauna it passes up into the true 

 Ordovician (Black River, Trenton, and Richmond) without kno^vn 

 passage through the Ozarkian fauna, but that where the Upper Cambrian 

 is thin and characterized by an Ozarkian fauna it is overlain directly 

 and without angular unconformity, sometimes even without easily ob- 

 servable disconformity, by the Devonian. The latter condition of affairs 

 is, however, characteristic only of the eastern margin of the Rocky Moun- 

 tain belt, though it persists along this eastern margin from Roche Miette 

 on the north almost to the International Boundary, a distance of 335 

 miles. 



(§ 6c?.) In the Mount Robson region, central ^\ith respect to the entire 

 Rocky Mountain belt, the Upper Cambrian is fairly thick, but passes 

 upward into rocks carrying faunas comparable with certain phases of the 

 Ozarkian. On the eastern edge of this portion of the Rocky Mountain 

 belt, however, the LTpper Cambrian of Roche Miette is thin, carries 

 Ozarkian faunas, and is overlain directly by the Devonian, as it is in the 

 Sawback Range and in the vicinity of Lake Minnewanka, on the Cana- 

 dian Pacific 200 miles to the south. If the analogy between the two 

 sections (Canadian Pacific and Grand Trunk Pacific) holds and Ave are 

 right in the generalization which we have made fqr the Canadian Pacific 

 Railway section, we might expect to find true Ordovician in the fairly 

 central Mount Robson region. The presence of apparently Ozarkian 

 types near Mount Robson, where the rocks are surprisingly fossiliferous, 

 might on the other hand lead us to suppose that our generalization needs 

 certain modifications, and that we may have merely overlooked the 

 Ozarkian faunas in our collecting from the thick but relatively less fos- 



'Dowling: Summary Reyt. G^ol. Surv. Canada for 1911, pp. 205-208, 1012. 

 s Adams : Discovery of phosphate of Ume in the Rocky Mountains (of Canada), 

 Commission of Conservation. Canada, 1915, p. 13. 



° Schofield : Summary Rept. Geol. Surv. Canada for 1918, pp. 131-132, 1914. 

 10 Walcott : Smithsonian Misc. Coll., vol. 64, 1916, p. 271. 



