24 C. D. WALCOTT ALGONKIAN FORMATIONS OF MONTANA 



nearly complete substitution of clastic materials for the limestones of its 

 eastern development. 



"In the vicinity of Shuswap lakes and on the western border of the Interior 

 plateau, the beds overlying the Nisconlith and there occupying the place of the 

 Selkirk series are found to still further change their character. These rocks 

 have been named the Adams Lake series.* They consist chiefly of green and 

 gray chloritic, felspathic, sericitic, and sometimes nacreous schists, greenish 

 colors preponderating in the lower and gray in the upper parrs of the section. 

 Siliceous conglomerates are but rarely seen, and on following the series be- 

 yond the flexures of the mountain region it is found to be represented by 

 volcanic agglomerates and ash beds, with diabases and other effusive rocks, 

 into which the passage may be traced by easy gradations.t The best sections 

 are found where these materials have been almost completely foliated and 

 much altered by dynamic metamorphism, but the approximate thickness of 

 this series is again about 25,000 feet."| 



Of the section along the International boundary, Doctor Dawson 

 wrote :§ 



"A thickness of at least 11,000 feet of sandstones and shales of red, gray, and 

 greenish colors, frequently alternating and including several contemporaneous 

 trap flows, occurs between the Continental watershed and the Flathead river. 

 This series has not been traced into connection with the sections previously 

 described, but it shows some resemblance to the Selkirk and Castle Mountain 

 groups. The occurrence of blackish calcareous argillites and sandstones at 

 the base may indicate the presence of the Bow River series there, while a 

 limestone at the top of the section in this part of the mountains may prove to 

 be that of the Castle Mountain group." || 



Doctor Dawson considered all of the Adams Lake and Nisconlith series 

 to be of Cambrian age. From the known presence of 'upward of 30,000 

 feet of pre-Cambrian unaltered sediments in Montana and Idaho, on the 

 strike of the strata of the Adams Lake and. Nisconlith series, it appears 

 to be more probable that the Nisconlith and most of the Adams Lake 

 (Selkirk) series are of pre-Cambrian age and to be correlated with the 

 Belt terrane^f as developed in northwestern Montana and northern 

 Idaho. 



During the season of 1904 Dr Keginald A. Daly, of the Geological 

 Survey of Canada, studied the section on the line of the International 

 boundary, between the Kootenay river, at Port Hill, Idaho, and the east- 



* For the Selkirk and Adams Lake series see references above given for Nisconlith 

 series. 



t Annual Report Geological Survey of Canada, vol. vii (N. S.), p. 35 B. 



t Comprising greenish schists 8,100 feet, grayish schists 17,100 feet. In Bull. Geol. 

 Soc. Am., vol. 2, p. 1G8, the thickness is given in error at half the above. 



§ Loc. cit., p. 68. 



|| Annual Report Geological Survey of Canada, vol. i (N. S.), pp. 50 B, 51 B. 



H Belt terrane is here used to include the entire series of Algonkian rocks as found 

 in the Belt mountains and westward in Montana and Idaho. 



