53 



granite magma accompanied or followed the principal 

 erogenic movements which affected the Purcell range. 

 Cutting the granite itself as well as the sediments in the 

 neighbourhood of the granite, are aplite, lamprophyre, and 

 pegmatite dykes which record the last known igneous 

 activity in the Purcell range. 



PLEISTOCENE DEPOSITS. 



Lying unconformably on the old eroded surface 

 of all the bed rock formations is a partly consolidated 

 stratified series of clays and sands, into which the streams 

 have incised their beds, leaving well developed terraces 

 at various elevations above their flood plains. In the neigh- 

 bourhood of the St. Eugene mission two seams of lignite 

 are found in the stratified clays of the Pleistocene. 



REGIONAL STRUCTURE. 



The Rocky Mountain geosyncline, which includes 

 the greater part of the Selkirk, Purcell, and Rocky Moun- 

 tain ranges, consists of Pre-Cambrian, Palaeozoic, and 

 Mesozoic sediments. Their western border passes through 

 Coeur d'Alene, Kootenay, and Shuswap lakes, along 

 whose shores is exposed the old crystalline complex, from 

 which part of the above sediments was derived. 



The Rocky mountains on the east are separated 

 from the Purcell range on the west by the wide Kootenay- 

 Columbia valley. This topographic feature, which is of 

 first importance in the structure of the region, is called 

 the Rocky Mountain trench. The rocks which form the 

 greater part of the Purcell range are probably Pre-Cam- 

 brian in age, and their structure is of an entirely different 

 character to that of the Rockies. The Purcell sediments 

 were first folded into a series of northerly plunging anti- 

 clines and synclines. Later these folds were truncated by 

 normal faults which strike in a N.E-S.W. direction and 

 hence trend in a direction at right angles to those of the 

 Rocky mountains. It is probable also that the fault 

 system of the Rockies truncates that of the Purcells, for, 

 in the Rocky Mountain trench, a block of Mississippian 

 limestone is down-faulted in contact with the Pre-Cam- 

 brian quartzites, and this block trends in a N.W.-S.E. 

 direction. From the above facts it is probable that the 



