[schofield] 



ROCKY MOUNTAIN TRENCH 



73 



DiSCONFORMITY 



Pre-Cambrian. 



In contrasting the stratigraphy of the two flanks, it will be seen 

 that the chief difference lies in the fact that on the eastern flank the 

 Jefferson limestone lies conformably on the Elko formation while on 

 the western flank in the Purcell Mountains, the Jefferson limestone 

 lies with an apparent disconformity on the Gateway formation with 

 the result that on the western flank the Phillips, Roosville, Burton, 

 and Elko formations are missing. 



Structure at the 49th parallel. 



Daly^ makes this reference to the structure of the trench (Fig. 1) 

 at the 49th parallel: "Between Gateway and the summit of the 

 McGillivray range (the most easterly subdivision of the Purcell 

 Mountains) the Kitchener (Siyeh) and Purcell lava beds are warped 

 into a broad unsymmetrical anticline. The dips average 35 degrees 

 N.E. on the eastern limb, a steepness which would rapidly carry the top 

 of the Purcell series of sediments far below the level of the Devonian 

 limestone at Tobacco Plains. The distance between the limestone and 

 the most easterly outcrops of Purcell Lava across the drift-covered 

 Rocky Mountain trench is eight miles. We can only conjecture the 

 structures beneath the drift cover. Those actually visible indicate 

 that the Rocky Mountain trench is at the boundary line located on 



1 Daly, R. A., Geol. Surv., Can., Mem. 38, 1912, pp. 112-137. 



