I'KK-CAMnRlAX ROCKS Ol' Till-; I'.OW \•.\LLi■;^■ WAI.COTT 427 



angular fragments of the subjacent pre-Cambriaii formations (fig. 

 I, pi. 46). The Cambrian sea was evidently transgressing across the 

 dark siliceous shales of the pre-Cambrian land and reducing them 

 to rolled pebbles, angular fragments, and mud. The mud gave ori- 

 gin to small lentiles of shale similar in character to the shale below 

 the unconformity, while lentiles of sandstone of greenish tint indicate 

 that fine material was being derived from still older pre-Cambrian 

 formations than the shale. 



On the southwest side of the Bow \'alley the Fairview formation 

 extends well down on the wooded slopes, but I know of no exposure 

 showing the contact of its basal conglomerate with the underlying 

 Hector shale north of Mount Temple. East of Mount Bosworth 

 the contact of the Cambrian and pre-Cambrian appears to be in the 

 valley just north of Stephen on the Continental Divide. 



Of greater importance is the evidence that the sediments of the 

 two periods were deposited under different physical conditions. The 

 Cambrian sandstones are composed of clean, well-washed grains, 

 and the Cambrian calcareous and argillaceous shales were deposited 

 as muds offshore along with the remains of an abundant marine 

 life. The Hector shales of the pre-Cambrian are siliceous and with- 

 out traces of life ; the sandstones are impure and dirty, with the 

 quartz grains a dead milky white, or glassy and iron stained. The 

 sediments forming them were evidently deposited in relatively quiet 

 muddy waters, and I think in fresh or brackish waters.^ 



I do not compare the limestone formations, as they are 2,000 feet 

 or more above the plane of unconformity in the Cambrian, and be- 

 low the Hector-Corral Creek series in the Algonkian. 



PRE-CAMBRIAN ROCKS 



The distribution of the ])re-Cambrian rocks in the Bow Valley is 

 outlined on the accompanying map (pi. 47). They extend through- 

 out the bottom and lower slopes of the valley from Bow Peak to 

 Cascade, on the Canadian Pacific Railway, about 7 miles west of 

 Banff. East of Mount Hector and in the Mount Richardson-Ptarmi- 

 gan Peak mass they rise in high hills both east and west of Pipestone 

 River, and continue eastward across Corral and Baker creeks before 

 passing beneath the Cambrian, on the south slopes of Castle Moun- 

 tain. 



' This view will be presented more fully in a paper on "The Ahrupt Appear- 

 ance of the Cambrian Fauna in North .\merica" that T have prepared for 

 presentation at the meeting of the International Geological Congress at Stock- 

 holm in August, 1910. 



