100 J. Parkinson — Lake Basins in Alberta ^ British Columbia. 



on the Fraser and Thompson Eivers in British Columbia, from 

 2,400 to 3,000 feet. Of these he says : " Many of the higher are 

 accumulations along the shore of a great sheet of water ; most of the 

 lower have been carved out of deposits which at one time filled 

 the valleys from rim to rim, and more or less completely levelled 

 up the broken surface of the country, by the gradually receding 

 waters of a lake or of the sea, and eventually by the rivers them- 

 selves deepening their channels to their old pre-Glacial levels " 

 (p. 112). He concludes that the interior of British Columbia was 

 submerged 4,000 to 5,000 feet during the formation of the Boulder- 

 clay (p. 108). 



The second hypothesis ascribes sufficient erosive power to a glacier 

 in descending a sharp declivity such as the cirque at the head of 

 Lake Agnes. Such plunging action is appealed to by Professor 

 Bonney to explain the rock basins of Lakes Cadagno, Tremorgio, 

 and others on the Lepontine Alps. In the case of Lake Agnes 

 a glance at the map shows that here is ample gathering-ground for 

 ice. The line of the Continental watershed lies a mile and a half 

 to the west, with summits ranging, in the case of Pope's Peak, to 

 9,595 feet. Mount St. Piran, to the north, has a height of 8,580 feet. 

 These between them form the north and north-north-west walls 

 of the tarn. If any erosive action can be ascribed to ice, the 

 present instance would afford an excellent opportunity for the 

 display of its power, and it is quite possible that this is the true^ 

 explanation. 



At the time of my visit to Lake Agnes a third possibility 

 occurred to me which may have some value, at least, as a con- 

 tributory cause. The quartzite forms the lower bed in the walls 

 of the lake, and must also occupy its floor, for the little waterfall 

 of discharge passes over it for some distance below the level of the 

 lake surface. The superincumbent beds are of a slaty nature, rather 

 finely bedded, and broken. This, taken in conjunction with the 

 dip of the whole up the lake, seemed to me to make it at least 

 possible that the ordinary agents of denudation in working out the 

 valley and its cirque-like head might form a basin which would 

 retain water, simply from the fact that there was a greater thickness 

 of less resisting material at the upper than at the lower end. I put 

 this on record merely as a suggestion, but we may perhaps suppose 

 some such process as the following. In early days the valley would 

 incline steeply down to its lip, its bottom occupied by a stream 

 attaining at certain times of the year to the dignity of a torrent of 

 some dimensions. When worn down at its lower end to the level 

 of the more resisting quartzite, the erosive action of the water would 

 be checked at that point, but the constant freshets concentrated on 

 its upper end by reason of the cirque-like disposition of the clifi' 

 would prevent the removing power of the water being materiallj'^ 

 lessened at the valley head. This process would go on possibly 

 with increasing slowness, but with a tendency analogous to that 

 ascribed to a glacier in descending a steep slope. 



My sincere thanks are due to Professor Bonney for his kindness 



