NO. 5 PRE-DEVONIAN PALEOZOIC FORMATIONS 23 1 



Troughs. They are compact, hard, and, on weathered surfaces, rough 

 and often dark, although on a fresh break they are Hght and medium 

 Hght gray in color. They do not have the smooth, weathered surface 

 of the Ottertail, Mons, and Stephen limestones, but are more like 

 the Middle Cambrian Eldon, and Silurian Beaverfoot limestones. 



The absence of fossils in the upper i,ooo feet (304.8 m.) or more 

 of the Lyell limestones favors the view that during the period of its 

 deposition, conditions were unfavorable for their preservation. The 

 deposition of the calcareous deposits forming the Lyell limestones 

 abruptly ceased, except at Tilted Mountain, where the argillaceous 

 and calcareous muds accumulated in the shallow seaways and contain 

 the fauna of the Upper Cambrian Sabine formation. This same order 

 of events occurred in the Glacier Lake, Sawback, and Beaverfoot 

 Troughs. 



Mr. J. F. Walker, in his instructive and valuable memoir on the 

 Windermere map area,' correlates the Lyell limestones of the Beaver- 

 foot Trough as they occur in the Stanford Range with the Ottertail 

 limestones of the Goodsir Trough. I think that this correlation is not 

 sound for the following reasons : 



1. The Lyell limestone is a rather coarse, rough-weathering, hard, 

 more or less magnesian limestone with a very meager marine fauna 

 below, and none, as far as known, in the upper 1,000 feet (304.8 m.) 

 or more of its thickness. 



2. The Ottertail limestone is described by Allan as follows : ^ 



This formation is, in general, a lithological unit, being composed essentially 

 of limestone, massive and thin-bedded, with intercalated layers of calcareous 

 shale. The shaly character of the beds is more evident towards the base of the 

 formation. On a fresh surface the rock composing the whole band is charac- 

 terized by its grey or bluish colour, while on weathered faces it is light grey 

 to black. The shale bands are so distributed between the more massive beds 

 that they do not greatly affect the steepness of the slope on the exposed face. 



Fragmentary remains of brachiopods and trilobites occur through- 

 out the Ottertail, and entire specimens are not uncommon. 



In weathering, the hard Lyell limestones break down into angular 

 blocks and fragments and the Ottertail limestones into a debris slope 

 of slabby limestone and large blocks mixed with calcareous shale. The 

 Ottertail formation is underlain by the readily disintegrated Chancel- 

 lor shale, which, by undermining, causes the Ottertail to form high, 

 clean-cut cHfifs (see pi. 75). 



' Geol. Surv. Canada, Mem. No. 148, 1926, pp. 21, 22. 

 '^ Geol. Surv. Canada, Mem. No. 55, 1914, p. 87. 



