NO. 5 PRE-DEVONIAN PALEOZOIC FORMATIONS 243 



Character. — Massive-bedded, dark bluish-gray limestones 60 feet 

 (18.3 m.) at the top, with thick layers of gray oolitic limestone with 

 interbedded bands of green siliceous shale below. 



Thickness. — At Mount Bosworth, 360 feet (109.7 ^•)- 



Geographic distribution. — Known only at Mount Bosworth, Paget 

 Peak, and northwest along the Continental Divide to Mount Daly. 



Stratigraphic relations. — This formation might be included with the 

 Sherbrook, as its upper 60 feet (18.3 m.) of heavy, blue limestone 

 is underlain by 300 feet (91.4 m.) of gray oolitic beds much like the 

 oolitic limestone of the Sherbrook. There are no diagnostic forms 

 that serve to distinguish it from the Sherbrook fauna. My reason for 

 separating it as a distinct formation was because it forms a marked 

 topographic feature on Mount Bosworth and on Paget Peak. 



Bosworth Formation. Walcott, 1908' 



Type locality. — South side of Mount Bosworth on the Continental 

 Divide above Kicking Horse Pass. 



Derivation of name. — From Mount Bosworth. 



Character and thickness. — Alternating bands of thick, shaly layers, 

 and thin layers of dolomitic limestone, with 48 feet (14.6 m.) of 

 intercalated siliceous shale, forming a series 1,587 feet (483.7 m.) 

 thick on Mount Bosworth. 



At Castle Mountain, 20 miles (32.2 km.) southeast of Mount Bos- 

 worth, the formation has a thickness of 423 feet (128.9 ni.). In the 

 Ranger Canyon section of the Sawback Range, 10 miles (16.1 km.) 

 south-southeast of the Castle Mountain section, 165 feet (50.3 m.) 

 of gray oolitic limestone is referred to it, and at Cotton Grass Cirque, 

 II miles (17.7 km.) north of Castle Mountain section, the Bosworth 

 is represented by 500 feet (152.4 m.) of limestone, arenaceous lime- 

 stone, and shale. On Ghost River, 32 miles (51.5 km.) east of Castle 

 Mountain, it is entirely absent through non-deposition. The upper 

 strata of the Bosworth in the Sawback Range sections vary from thin 

 layers of gray oolitic limestones interbedded in arenaceous shales to 

 alternating beds of shale and thin layers of compact sandstone. 

 No evidence of an unconformity was observed at the summit of the 

 Bosworth, but a disconformity exists by non-deposition of the Paget, 

 Sherbrook, and more or less of the upper part of the Bosworth in the 

 Sawback Range area. 



Geographic distribution. — The Bosworth is a formation that was 

 largely deposited in the central area of the Cordilleran Geosyncline ; 

 ^ Loc. cit., pp. 205, 208. 

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