SILURIAN. 



The Silurian is composed of light-coloured, thin- 

 bedded, yellow limestones. In the region to the east of 

 Lake Manitoba important beds of gypsum are being mined 

 from this formation. 



DEVONIAN. 



In Manitoba the Devonian rocks are divisible into 

 three series as below : — 



Upper Devonian or Manitoban, consisting 

 of light gray, hard brittle limestone, 

 with red argillites at the base, 

 about 200 feet (64 m.) 



Middle Devonian or Winnipegosan, con- 

 sisting of light yellow, hard dolo- 

 mite, with porous beds beneath, 

 about 200 feet (64 m.) 



Lower Devonian, mainly red shales. 

 These beds probably represent only 

 the upper part of the lower Devonian 

 of eastern America, about 100 feet (30 m.) 



In western Saskatchewan these beds may be found 

 near the Churchill river; having nearly the same characters. 



In Alberta, the most eastern exposure is in the neigh- 

 borhood of Athabaska river. In the Rocky mountains 

 they form the Intermediate series, brownish, irregularly 

 hardened dolomites, and greyish, crystalline dolomites, 

 with some sandstones and quartzites. 



CARBONIFEROUS. 



These rocks are found in South Dakota, Montana, 

 and Alberta. They are not exposed in Manitoba or along 

 the northwest margin of the Cretaceous plateau, but are 

 confined to the Rocky Mountain region. They have been 

 subdivided on lithological grounds into upper and lower 

 Banff limestones. These formations are each capped by 

 shaly beds, from which have been obtained a few charac- 

 teristic fossils. The formation is generally a bluish 

 limestone, and forms the summits of Cascade and Rundle 



