NO. 5 PRE-DEVONIAN PALEOZOIC FORMATIONS 255 



cliff on Wedgewood Peak of the Mount Assiniboine massif, and 

 it occurs in the cliffs of Mount Sedgwick above the Siffieur River, 

 80 miles (128.7 km.) northwest of Assiniboine. The McNaughton 

 sandstones of the Robson Peak section, 125 miles (201.1 km.) north 

 of Mount Sedgwick, may represent the Fort Mountain in that area. 



Fauna. — A few annelid trails and borings. 



Observations. — The Fort Mountain formation represents the beach 

 sands of the transgressing early Cambrian sea and probably occurs at 

 the base of sections whenever the waters of the Lower Cambrian 

 covered the irregular surface of the pre-Cambrian rocks that formed 

 the bottom of the sea. At Redoubt Mountain and on Little Vermilion 

 Creek northeast of Vermilion Pass, fine arenaceous conglomerates 

 are superjacent to the pre-Cambrian, but in other localities where 

 the pre-Cambrian surface was finely disintegrated the basal beds may 

 be shales or fine sandstone. 



Mahto Formation. Walcott, 1913* 



Type locality. — Mahto Mountain, between Calumet Creek and Cole- 

 man Brook in the northern part of the Robson Peak District. 



Derivation.- — From Mahto Mountain. 



Character. — Massive-bedded quartzitic sandstones, with some thin 

 layers of hard, compact sandstones and a few thin bands of dirty 

 grayish-brown arenaceous shale. 



Thickness. — On Tah and Mahto Mountains, southwest of Moose 

 Pass, 1,800 feet (548.6 m.). 



Geographic distribution. — Northeastern face of Mahto Mountain, 

 and northwestern, north, and northeasterly slopes of Tah Mountain. 

 A survey of the Moose and Smoky River area will undoubtedly 

 extend the area of the formation to the northwest and southeast. 



Tah F"ormatiO'N. Walcott, 1913'' 



Type locality. — Tah Mountain at Moose Pass, Robson Peak District. 



Derivation. — From Tah Mountain. 



Character. — Hard, siliceous, green and purple colored shales, with 

 irregularly intercalated beds of compact, purple and gray limestone 

 in central portion. 



Thickness. — At Tah Mountain, 800 feet (243.8 m.). 



^ Smithsonian Misc. Coll., Vol. 57, No. 12, p. 335. 

 ' Idem. 



