123 



Tentative Columnar Section of the Shuswap Series. 



Thickness. 

 Top, erosion surface. Feet. Metres. 



Adams Lake formation; greenstone schists. 10,000 3,048 

 Tshinakin formation: 



Limestone (1,500 ft., 457 m.) 

 Phyllitic metargillite (800 ft., 244 m.) 

 Limestone (1,600 ft., 488 m.) 



Total 3,900 1,188 



Bastion schists, phyllite with green schists 



at top 6,500 1,981 



Sicamous limestone 3,200 975 



Salmon Arm schists, nr'caceous 1,800 547 



Chase quartzite 3,000 914 



Tonka watla paragneiss 1,500+ 457 + 



Base concealed 



29,900 9,111 



The Tonkawatla formation is exposed in a series of 

 railway cuts 3 miles (5 km.) west of Revelstoke. It con- 

 sists of a dark-coloured, massive, homogeneous, compara- 

 tively fine-grained gneiss bearing thin interbeds of white 

 crystalline limestone. The latter are seldom over 2 inches 

 (5 cm.) in thickness but are locally numerous. Their 

 presence suggests that the whole group of rocks here 

 exposed is of sedimentary origin. The gneiss is rich in 

 biotite and plagioclase and is probably best interpreted as 

 originally a calcareous argillite. The paragneiss passes 

 upward into yet more massive, harder biotitic quartzite, 

 which also carries thin intercalations of limestone. 



Quartzite of identical habit and tentatively ascribed 

 to the same horizon, is exposed on the slope due south of 

 Shuswap station near the village of Chase. Here the 

 thickness is to be measured in hundreds of metres and a 

 special name, Chase quartzite, has been given to the mem- 

 ber. Besides the thin beds of limestone, the quartzite 

 often shows abundant disseminated grains of carbonate, 

 largely calcite. 



At Shuswap station the massive Chase quartzite is 

 directly overlain by coarse, glittering muscovite-biotite 

 schist, often garnetiferous and seamed with beds of mica- 

 ceous quartzite. As usual in the Shuswap series, the planes 



