STRATIGRAPHY ALONG THE ROCKY MOUNTAIN TRENCH 375 



even where the intrusions are absent metamorphism is found to 

 vary greatly. In the Selkirk Range along the main line of the 

 Canadian Pacific Railway, where there are no intrusives, the 

 upper Paleozoic Laurie formation contains the same type of semi- 

 metamorphic beds as are found farther east in the lower portions of 

 the Cambrian. Many of the upper Paleozoic rocks of the Arrow 

 Lake region are more metamorphosed than the pre-Cambrian 

 (or early Cambrian) beds to the east in the Cranbrook area. This 

 last case is probably explained by contact metamorphism. 



A quartz grit having well-rounded quartz pebbles and a cal- 

 careous cement was found in several places along the west side of 

 the trench in the vicinity of Lake Windermere. This formation 

 was associated with argillaceous rocks which varied from shales to 

 schists in the different localities, although it most likely represents 

 the same horizon because of its very distinctive characteristics, 

 which were not found in any other formation. 



At Sinclair Springs there is a bed of highly crystalline limestone 

 which is higher in the stratigraphic series than another limestone 

 which is not crystalline. So many similar cases were found that 

 it seems as though the anamorphic influences along the trench 

 were very irregular. The cause of this irregularity is varied. 

 In the southern Purcells, the intrusions are chiefly responsible. 

 Farther north the intrusives rarely appear at the surface, but 

 their presence below the surface is shown by the hydrothermal 

 alteration of the rocks in many places along the west side of the 

 trench. In the northern portion, however, the most important 

 anamorphic results are connected with diastrophic movements. 

 In the vicinity of large faults the alteration is often more pro- 

 nounced than elsewhere. The Purcell Range was probably deformed 

 at two periods'" so that the formations on that side would tend to be 

 differently metamorphosed from those of corresponding age on the 

 other side. At present the exposed pre-Cambrian and later forma- 

 tions are found at the same general level, but formerly the pre- 

 Cambrian was more deeply buried. As deformation went on, the 

 pre-Cambrian was brought gradually toward the level of the 

 younger formations by folding and faulting. After the two reached 



' S. J. Schofield, Geol. Sun. Can. Mem. 76, p. loi. 



