l62 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 75 



stones and shales and 1,122 feet (341.9 m.) of Middle Cambrian 

 limestones represent the eastern extension of the Middle Cambrian 

 limestones of the Mt. Bosworth and Mt. Stephen area, where they 

 are 5,244 feet (1,598.4 m.) thick. No sediments of Upper Cambrian 

 or Ozarkian age appear to have been deposited in this eastern area. 



Extent of Bozv Trough. — The seaway of the Trough was probably 

 from 50 to 60 miles (80.5 to 96.5 km.) in width, at the time of its 

 greatest development. Its extension to the south-southwest appears 

 to have been limited by the pre-Cambrian Kintla Island uplift,' but 

 it was undoubtedly connected on the south with an open seaway, as 

 yet unrecognized, of the Cordilleran Geosyncline, for the Lower and 

 Middle Cambrian faunas of Utah and Nevada are closely related to 

 those of the Bow Trough Lower and Middle Cambrian formations. 

 To the north-northwest of the Bow Valley, similar characteristic 

 faunas of Lower and Middle Cambrian age have been found 42 miles 

 (67.6 km.) distant in the Glacier Lake, Saskatchewan area, also in the 

 Robson Peak District 167 miles (268.7 ^^'"''•) fi'om the Bow Valley. It 

 is probable that the Bow Trough was an open seaway from the Bow 

 \^alley to the Saskatchewan area in Lower and early Middle Cambrian 

 time, for the Lower Cambrian St. Piran and Mt. Whyte formations, 

 the Middle Cambrian Cathedral limestones, and a representative of 

 the Stephen formation (Murchison) occur in Mt. Sedgwick (D on 

 map, see figs. 20, 21, p. p. ?), but the great Eldon limestone is absent. 

 The Arctomys shales which followed the close of the Middle Cam- 

 brian have a large development at Glacier Lake, gradually thinning 

 out to the southeast in the Saw back Range (F and H on map) and 

 on Mt. Bosworth (R on map) in the Bow Trough. With the 

 Arctomys, the formations common to the Bow Trough and the 

 Saskatchewan area terminate, unless the fauna of the Upper Cam- 

 brian Sullivan formation be found later to be similar to that of the 

 Bosworth of the Bow Trough sections, in which case the Bosworth 

 will be the last of the Bow Trough formations deposited in the 

 Saskatchewan area. 



A band of limestone 165 feet (50.3 m.) thick beneath the Lyell 

 formation in the Saw back Range (H on map) may represent the 

 Bosworth, but a thickening of this band, 18 miles (28,9 km.) farther 

 to the north-northwest in the Range, to 500 feet (152.4 m.) leads to 

 the inference, in the absence of fossils, that it is a thinning out of 

 an extension of the Sullivan from the northwest rather than the ex- 

 tension of the Bosworth to the northwest. 



' Smithsonian Misc. Coll., Vol. 53, No. 5, p. 19L 



