[MACKENZIE] HISTORICAL AND STRUCTURAL GEOLOGY 101 



place in the upper Triassic. In the early stages of this subsidence, it 

 is supposed that part of the sandy mantle of the land was concentrated 

 to form the quartzose sandstone which has been assigned to the 

 Triassic. Following this, by reason of increased subsidence, marine 

 waters gained access to the region, in the form of a sea trending north- 

 northwest and south-southeast, and extending at least as far south 

 as, and probably beyond the 49th parallel. From the varying thick- 

 nesses and uniform character of the sediments formed (the Fernie 

 formation) it is apparent that great volumes of fine mud were deliv- 

 ered to this sea by rivers flowing from low land to the west, and 

 there may have been several large estuaries along the western edge 

 of the marine basin of that time. The sea was probably never very 

 deep, judging from the occurrence of the reptilian remains which have 

 been found in three localities (2, a), one of which is within the area 

 under consideration (17, a), (24, a). The combination and attitude 

 of the bones at this place indicate only a small amount of transporta- 

 tion. A thin bed of a greenish rock which McLearn has termed tuff 

 (27, a) occurs in the Fernie formation. If its designation as tuff be 

 correct, it marks the first evidence of igneous action in the Rocky 

 Mountain area since the Precambrian Purcell lavas. It was in this 

 bed that the reptilian bones were found in 1912. 



The Fernie is transitional into the overlying Kootenay formation 

 (24,a), (27, b) and there is apparentlyno cessation of deposition recorded, 

 yet the marine waters must have gradually withdrawn, and wide- 

 spread freshwater lake basins must have succeeded them. In these 

 shallow lakes the Kootenay measures were laid down. 



The conditions of Kootenay time may be interpreted from the 

 nature of the sediments. Westward from the present Kootenay 

 river stretched an undulating land, of moderate relief, extending 

 hundreds of miles to the north-northwestward, and drained by many 

 eastward flowing streams of moderate gradient. This land was being 

 uplifted. The bedrock of the terrane in the eastern portion of this 

 region was limestone, probably Pennsylvanian in age, and was mantled 

 with residual chert in fragments of varying size. Farther west the 

 quartzites and argillites of the lower Palaeozoic and the Precambrian 

 were exposed, but there is no evidence of plutonic rocks occurring at 

 the surface in this westward land at this time. Eastward as far as 

 the present edge of the great plains, and parallel to this land, extended 

 a low, marshy plain, its surface covered with shallow lakes, which 

 slowly but continually shifted their positions, aided by periodic 

 risings of the rivers over this area, which was in effect the coalescent 

 flood-plain of many streams. Into these lakes through the agency of 



