185 



CRETACEOUS. 



Lower Ribboned Sandstone. — The Cretaceous beds 

 are exposed along the eastern base of Cascade mountain. 

 The Lower Ribboned sandstone consists of alternating 

 bands of brown-weathering sandstone and shale. This 

 formation follows the bottom of the Cascade trough and 

 is exposed on the road between Bankhead and the west 

 end of Lake Minnewanka. The beds are here about 

 1,000 feet (305 m.) thick. 



Kootenay Coal Measures. — This formation consists 

 of 2,800 +feet (853+ m.) of sandstone and shale enclosing 

 several workable seams of coal. There are fourteen seams 

 exposed at Bankhead, where the coal is being mined, and 

 nearly twice as many have been found at Canmore down 

 the Cascade trough. The coal is bituminous and anthra- 

 citic. Several of these seams are being mined at Canmore. 

 The coal measures are well defined between two massive 

 sandstone bands which form roof and floor. 



Upper Ribboned Sandstone. — This formation con- 

 sists of thin-bedded sandstones and shales. It is exposed 

 at the eastern base of Cascade mountain. The beds are 

 wedged between the coal measures below, and a thrust 

 plane above. Some of the uppermost Cretaceous beds 

 were planed away when the older beds were thrust 

 over them. There are about 550 feet (168 m.) 

 of beds exposed in Cascade mountain, but this formation 

 becomes thicker where it is exposed to the northwest and 

 southeast of this section. 



POST-CRETACEOUS. 



Igneous Complex. — The only igneous rock in the 

 Rocky Mountain section is represented by the Ice River 

 intrusive complex, which has the form of an asymmetrical 

 laccolith with a stock-like conduit. It has an area of 

 about 12 square miles (31 sq. km.). 



The rocks of the complex are all alkaline in composi- 

 tion, ranging from nephelite syenite and sodalite syenite 

 through urtites and ijolites, to a jacupirangite or alkaline 

 pyroxenite. These diverse types represent a complete 

 petrographic series with intermediate facies. 



The age of the intrusion is believed to be post-Creta- 

 ceous as determined by structural and correlation evidence. 



35069— 6|a 



