CORRELATION 319 



As regards thickness of the above described section, Dawson's figures 

 sum up 4,500 feet. Elsewhere * he says : 



"Between the eastern summit of the South Kootanie pass and the Flathead 

 river, the minimum estimated thickness of the outcropping Cambrian beds is 

 11,000 feet, but the section includes neither the summit nor the base of the series. 

 Other sections show a probable thickness of over 5,000 feet for a part of the series, 

 but none were found in which its whole volume could be ascertained." 



The writer's measure of the series which Dawson called Cambrian, 

 namely, the Altyn, Appekunn}^, and Grinnell formations, is 6,700 feet, 

 but, adding the Siyeh, Sheppard, and Kintla formations, is 10,700 feet, 

 which is an approximation to his estimate of 11,000. The latter three 

 formations occur in the section to which Dawson refers, and though he 

 elsewhere classed them as Carboniferous and Triassic, they are part of 

 the thickness which, in the quoted paragraph, he includes under Cam- 

 brian. 



Dawson notes an apparent unconformity between D (the Siyeh lime- 

 stone) and C (the Grinnell red beds) He says : f 



"In the almost vertical side of Sheep mountain the total exposed thickness of 

 beds of series C must be about 2,000 feet. These rest directly on the limestone B, 

 and are overlain by the limestone series D, the latter resting with evident uncon- 

 formity on them. This unconformity is shown very clearly by the existence of a 

 thick belt of bright red rocks, forming part of series C, which is observed to run 

 out altogether beneath the upper formation at one end of the mountain." 



The writer also observed this relation, but he interprets it as due to a 

 minor thrust rising from the Lewis major thrust which underlies Sheep 

 mountain. The structure was identical in appearance and position with 

 others seen traversing the Altyn formation in Yellow mountain Cfigure 

 6, page 335). It is also exceptional in the relations of division C to D, 

 which were observed throughout many miles as the conformable contact 

 of the Siyeh limestone on the Grinnell argillite. 



About the outlet of Waterton lake, the Cretaceous rocks are deeply 

 buried by drift and the outcrop of the Lewis thrust is obscured. The 

 unusual superposition of the ancient argillites and limestones on the 

 Cretaceous might well escape even so keen an observer as Dawson. He 

 did not visit Chief mountain or any other locality where the evidence 

 is clear. 



In 1875 Daw r son assigned no definite age to the rocks in question. 

 In 1885, after more extended experience in the Canadian Rockies, he 

 provisionally classified them as follows : 



♦Canada Geological Survey, Report 1885, p. 158 B. 

 t Canada Geological Survey, Report 1885, p. 41 B. 



