BRITISH COLUMBIA AND ADJACENT REGIONS. 



275 



and at a considerably lower elevation, reaching a maximum height 

 of about 1700 feet above the sea. In the vicinity of Kamloops 

 Lake and in the South Thompson and Okanagan valleys, it is well 

 shown, generally forming the first terraces above the rivers. In 

 origin it is probably, like that of the Nechacco region, a deposit from 

 the turbid waters flowing from glaciers at a time when these had a 

 considerable extension from the various mountain-ranges. At this 

 time, either from general depression of the land, or the damming 

 of the valleys by ice or moraines, a system of winding water-ways, 

 lakes or fiords, must have occupied the main valleys. The heads of 

 these valleys in the Gold ranges still hold long and deep lakes, on 

 the banks of which, where they have been examined (more parti- 

 cularly in the Shuswap region), drift deposits are comparatively un- 

 important, and the white silts are not found. The fine silty material 

 must have been deposited in somewhat tranquil waters ; but it 

 appears difficult to explain its absence from the valleys on the 

 flanks of the Gold ranges. It may be suggested that the currents 

 in the upper parts of the valleys were so strong as to prevent 

 the deposition of the silt; but, apart from the difficulty found in 

 supposing such great bodies of water as the valleys must have held 

 at this time to be in rapid motion, there is no such sudden widening 

 in the valleys at the points at which the silt commences as might 

 account for the slackening of the current. 



It is perhaps on the whole most probable that the basins now 

 occupied by the Shuswap lakes and others in a like position were 

 filled with giacier-ice, from which the water flowed down the long 

 valleys, while the abrasion of the rocky beds of the glaciers supplied 

 in large quantity the material of the silt deposits. From the height 

 at which the silts occur, their greater coarseness in the lower part 

 of the Okanagan valley, and the evidence of current-action in that 

 valley near Osoyoos Lake, it is probable that this depression has 

 served as the main outflow of the white-silt lake or sound. At the 

 last it would appear that the glaciers retreated with considerable 

 rapidity, becoming extinct or dwindling to nearly their present 

 size, and leaving the upper portions of the valleys which penetrate 

 the Gold ranges almost free from debris and ready to form the 

 basins of the lakes which now generally occupy them. 



The explanation here adopted to account for the existence of these 

 lakes will, I believe, be found applicable to many in other parts of 

 British Columbia, and is again referred to on a subsequent page. 

 It is the same advanced by A. Helland for Norwegian lakes *. 

 Whether any of the lakes in the region now in question lie in rock 

 basins of glacial formation has not been determined, as the valleys 

 below their outlets are generally filled to an unknown depth with 

 detrital materials. 



Observations north of the 5Ath parallel in British Columbia. 



An exploratory survey of the remote region lying between the 

 54th and 56th parallels in British Columbia and of part of the 

 * Quart. Journ. Geol. Soc. xxxiii. p. 165. 



