[MACKENZIE] HISTORICAL AND STRUCTURAL GEOLOGY 111 



1912 I observed a fault which I correlated with the Lewis thrust in 

 the North Kootenay pass and in the country south of it (24, a). 

 Later work by Stewart has confirmed this correlation (41, e) and his 

 map has filled the gap between my own work and that of Willis 

 and of Daly. 



Dr. Bruce Rose informs me in a personal communication that 

 the Lewis thrust continues northward from the North Kootenay pass 

 at least as far as Gould Dome, near latitude 50 degrees, and that it 

 may even extend fifty miles farther north to the Kananaskis river. 

 The field evidence in this region is not yet definitely worked out. 

 If it does not continue northward as a single thrust phase, the break 

 is represented by other similar overthrusts. 



In Montana, Campbell shows the outcrop of the thrust surface 

 extending southward to the southern edge of the Glacier National 

 Park (9, a). The known length of the fault, measured in the general 

 direction of its outcrop, without regard to the sinuosities of its course, 

 is 50 miles in Montana and 85 miles in Alberta, 135 miles in all. Its 

 total length, however, is somewhat greater than this, for as mentioned 

 above it may extend northward for some miles from Gould Dome, 

 and it probably runs south of its southern mapped position. In 

 Montana the general direction of the outcrop is north 30 degrees west, 

 except for the deep re-entrant at the southern end, where it runs 

 north 35 degrees east for 15 miles. As only the northern side of this 

 re-entrant is mapped, it is not known whether this is really a change 

 in the strike of the fault or a change in direction caused by topography. 

 In Alberta virtually the same direction of 30 degrees west of north is 

 maintained to the headwaters of Pincher creek, 30 miles north of 

 the boundary. From here the strike swings gradually more to the 

 westward, and runs about north 80 degrees west to the North Koote- 

 nay pass, a distance of 23 miles. Here it turns sharply due north 

 and maintains this direction to Gould Dome, except for an offset of 

 three miles to the westward in the Crowsnest pass. If the break 

 extends north of Gould Dome the strike is a few degrees west of 

 north. 



Characteristics . — From its southernmost located position to the 

 North Kootenay pass, a distance of about a hundred miles, the Lewis 

 thrust is found at or near the base of the front ranges of the Rocl<y 

 mountains, and, as Willis explains (45, g), the topographic relations 

 of the front ranges adjacent to the boundary are dependent on the 

 position and attitude of the thrust surface. North of the North 

 Kootenay pass the thrust lies behind the front ranges of the moun- 

 tains, these being the Livingstone range continued northward in the 



