246 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 75 



the massive Middle Cambrian Eldon limestone beneath to the quite 

 different magnesian limestones of the Upper Cambrian Bosworth 

 formation above. 



Thickness. — At the type locality near Glacier Lake, 1,386 feet 

 (422.4 m.) (pi. 26 at B). At Cotton Grass Cirque, 48.5 miles (78 

 km.) southeast of Glacier Lake section, 725 feet (220.9 "'''•)' ^^^^ i" 

 the Ranger Canyon section, 69 miles (no km.) southeast of Glacier 

 Lake. 95 feet (28.9 m.) (pi. 26 at H). The formation a])pears to 

 be represented by the lower 268 feet (81.7 m.) of the Bosworth 

 formation included in the Mount Bosworth section of 1908,* which 

 is 42 miles (67.6 km.) south-southeast of Glacier Lake (pi. 26 at Q). 

 In the Robson Peak District, about 125 miles (201. i km.) north- 

 northwest of Glacier Lake, the Lynx formation of the Upper Cam- 

 brian has at its base 200 feet (60.9 m.) of shallow water arenaceous 

 shales that represent the Arctomys formation. The shales are super- 

 jacent to the Titkana limestones of the Middle Cambrian and at the 

 base of the Upper Cambrian. 



Geographic distribution. — Glacier Lake Canyon and headwaters of 

 Saskatchewan River. It occurs to the southwest in the Ranger Brook 

 Canyon section of the Sawback Range, and is represented at Mount 

 Bosworth on the north side of the Bow River Valley. The parti- 

 colored arenaceous shales at the base of the Lynx formation of the 

 Robson massif at Snow Bird Pass represent the Arctomys formation 

 in the Robson Peak District. 



Stratigraphic relations. — The Arctomys formation is definitely 

 bounded by the Upper Cambrian Sullivan formation above, and the 

 Middle Cambrian Murchison formation below, in the Glacier Lake 

 section, and its representative in the Sawback Range sections at 

 Cotton Grass Cirque, Ranger Brook Canyon, and Mount Bosworth 

 has the Upper Cambrian Bosworth above and the Middle Cambrian 

 Eldon formation below. In the Kicking Horse Pass section on Mount 

 Bosworth the Arctomys is clearly defined at its base where it re.sts 

 on the Middle Cambrian Eldon limestone, which does not appear to 

 be represented in the Glacier Lake section. 



MIDDLE CAMBRIAN . 



Eldon Formation. Walcott, 1908^ 



Type locality. — Southeast slope of Castle Mountain opposite Eldon 

 on the Canadian Pacific Railway. 

 Derivation. — From Eldon station. 



' Smithsonian Misc. Coll., Vol. 53, No. 5, 1908, p. 208. 

 ^Idem, No. i, p. 3. 



