[schofield] rocky MOUNTAIN TRENCH 81 



southwest at comparatively high angles, and overlie beds of garnet- 

 iferous schists, some of which contain large crystals of staurolite. 

 These in turn overlie beds of impure crystalline limestone, resting on 

 mica schists, the sedimentary origin of which is revealed by weathered 

 surfaces where rounded grains of quartz can be detected. A similar 

 section was seen at other points on the same side of the trough, and 

 the author suggests as an alternative hypothesis that, the schists and 

 gneisses are the metamorphosed equivalents of the grey quartzites 

 which occur in the Castle Mountain series; while the trough may have 

 been eroded along the outcrop of the soft calc schists at the base of the 

 formation. In a region where faults are numerous the evidence to 

 support this hypothesis is far from being conclusive. The gneisses are 

 cut by large dikes of pegmatite holding crystals of muscovite, some of 

 which measure over 20 inches across." 



The writer's observations on this section, in 1918, showed that 

 the rocks exposed in the floor of the trench were badly broken and 

 strong shearing had developed in a direction coinciding with the trend 

 of the trench. This shearing and crushing was later in age than the 

 metamorphism developed in the Shuswap rocks. It is considered to 

 be related in age to similar shearing and faulting which have been 

 determined in the trench to the south, although no direct evidence on 

 this point has been recorded. Before this is attempted a critical study 

 of the so-called Shuswap series must be completed and its position in 

 the geological column established. According to Malloch, the Bow 

 River series borders on the northeastern slope of the trough from Tête 

 Jaune Cache to the high mountain opposite the mouth of Goat River. 

 From this point northwards, the Castle Mountains series crosses the 

 river at the foot of Goat River rapids. On the northeastern flank, 

 gneisses and schists of the Shuswap series extend northwards as far as 

 Rau Shuswap River where they are succeeded by the rocks of the 

 Castle Mountain series. At Grand Canyon, Devonian rocks outcrop 

 and occur on both sides of the trough. 



The Age of Faulting in the Rocky Mountain Trench 



The faulting which occurs in the Rocky Mountain trench can 

 be correlated with that period of tension which follows the period of 

 compression in mountain building. It has the northwest-southeast 

 trend and characteristics of the other normal fault valleys in the 

 Rocky Mountains one of which, the Flathead valley, has been des- 

 cribed in some detail by Daly^ and Mackenzie.^ The Flathead valley 



1 Daly, R. A., Geol. Surv., Can., Mem. 38, 1912, p. 87. 



"^ Mackenzie, J. D., Geol. Surv., Can., Mem. 87, 1916, pp. 36 and 38. 



Sec. IV, Sig. 6 



