i8i 



Graptolite Shales. — These beds have been so named 

 by McConnell on account of the richness of certain layers 

 in graptolites. The presence of this fauna determines 

 the age of the formation as Ordovician. 



The Graptolite shales consist of black, carbonaceous, 

 and brown, fissile shale at the top, underlain by gray 

 shales which grade into the underlying Goodsir formation. 



The thickness of the formation varies and the lower 

 contact is ill-defined, but a thickness of at least 1,700 

 feet (518 m.) is represented. These shales occur as two 

 infolded bands in the Beaverfoot range. 



SILURIAN. 



Halysites Beds. — The Halysites beds consist chiefly 

 of dolomitic limestone and white quartzite. This forma- 

 tion lies conformably upon the Graptolite beds. The 

 character of the rock sharply distinguishes it from the 

 older strata. The formation is terminated above by a fault 

 contact or by an erosion surface. A measured section gave 

 1 ,850 feet (563 m.). The white quartzite is over 900 feet thick 

 (274 m.). It is infolded with the graptolite beds in the 

 Beaverfoot range. Some of the beds of dolomitic 

 limestone are highly fossiliferous; corals are most abundant, 

 but crinoids, brachiopods, and gastropods are also present. 



This is the youngest formation exposed to the west 

 of the Continental Divide, along this section of the Rocky 

 mountains. 



DEVONIAN. 



Intermediate Limestone. — This formation consists 

 of thin-bedded limestones, alternating with harder layers 

 of gray dolomitic and siliceous limestone, which on the 

 weathered surface becomes banded. In the Sawback, 

 Vermilion Lake and Cascade ranges it is exposed, being 

 repeated by reversed faulting. 



The thermal sulphur springs at Banff occur in the 

 Intermediate limestone. The rock is high in sulphur, 

 derived by the decomposition of pyrite which the lime- 

 stone contains; a strong odor of sulphide of hydrogen 

 is given off when the rock is struck with a hammer. 



Some of the beds are highly fossiliferous. Zaphrentis 

 and brachiopods are the most abundant forms present. 



