214 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 75 



Thickness. — Allan gives a thickness of 1,850 feet (563.8 m.) for 

 the Silurian of the Beaverfoot Range, which includes both the Brisco 

 and Beaverfoot formations. I estimated a thickness of 1,200 feet 

 (365.8 m.) for the Brisco formation as it occurs in the Brisco Range.* 

 Walker measured 759 feet (231.3 m.) in the Windermere map area.' 



Geographic distribution. — The Brisco limestones extend the entire 

 length of the Beaverfoot-Brisco-Stanford Range from the Kicking 

 Horse Canyon to Sabine Mountain. Mr. J. F. Walker reports them 

 from the north and south sides of Horsethief Creek in the Purcell 

 Range ' west of the Columbia River, and they occur in the high clififs 

 of the ridge between the Columbia and Spillimacheen rivers 10 to 20 

 miles (16 to 32 km.) south of Golden, British Columbia. It is 

 probable that the Brisco extends north of the Kicking Horse Canyon 

 but it has not been reported as far as known to me. 



Fauna. — Dr. Edwin Kirk reported that within 50 feet (15.2 m.) of 

 the base of the Brisco in the Windermere Creek section he found 

 Pentamerus sp., and a little higher stratigraphically Virginia sp. 

 occurred in abundance in the Sinclair Canyon section. In the upper 

 portion a more abundant fauna was collected near the head of Winder- 

 mere Creek which included : 



Halysites sp. 

 Syringopora sp. 

 Favosites sp. 

 Atrypina sp. 

 Spirifer sp. 

 Stropheodonta sp. 



In the argillaceous shale about 300 feet (91.4 m.) above the base 

 of the Brisco a graptolitic faunule occurs in which Dr. Rudolf Ruede- 

 mann identified : 



Monograptus cf. spiralis Geinitz 



Mo)iograpfus marri Perner 



Rctiolitcs (Gladiograpfus) gcinitaiamis Barrande 



Observations. — The Brisco is the most recent of the pre-Devonian 

 formations deposited in the Beaverfoot Trough and, as far as known, 

 in the Cordilleran Geosyncline. From its character, uniform bedding, 

 and thick layers, it was presumably deposited in clear water, with the 

 exception of a brief period when black argillaceous muds gave a 

 favorable habitat for a characteristic Silurian graptolite fauna. 



^Smithsonian Misc. Coll., Vol. 75, No. i, 1924, p. 11. 

 ^ Geol. Surv. Canada, Mem. No. 148, 1926, pp. 32, 2,2,. 

 ^ Loc. cit., p. 31. 



