REPORT OF TEE CEIEF ASTRONOMER 591 



SESSIONAL PAPER No. 25a 



reliefs formed in late Glacial time. Closely allied to these linear terracelets 

 are truncated fans which at various levels were washed from the principal branch 

 valleys into the trough and against the ice, the gravel-sand deposit in each 

 case backing up into the branch valley. A deltoid form was thus produced, 

 with the base of the delta marking the ice-wall which retained the detritus 

 on the side of the main valley. These high-level fans are themselves sometimes 

 terraced as if the ice-wall had lowered by successive stages. 



The wide benches slowly rising from Osoyoos lake to the mountains on 

 either side where their surfaces are about 200 feet above the lake level, are 

 composed of sandy gravel. This forms a thick, late-Glacial deposit. It has been 

 washed by slowly moving water, which has often ' leached ' out the finer debris 

 and left a thin cover of gravel over a great part of each bench. The details 

 of form suggest that the washing was performed by the waves and currents 

 of the lake during its expansion across the whole valley and during the slow 

 sinking of its level. Both climatic change and the down-cutting of the outlet 

 are responsible for the fall of the water. The maximum depth of the lake was 

 doubtless contemporaneous with the close of the Pleistocene period. Since then 

 the roughly graded valley-floor has been gullied by the small streams entering 

 the lake from east and west. Other channel-like depressions parallel to the valley 

 axis may represent the spill-ways of the waters derived from ice which, in late 

 Pleistocene time, was melting farther up the Okanagan valley. 



An interesting effect of glaciation is to be found in the peculiar drainage 

 re-arrangements in the lower part of the Similkameen river. The river passes 

 the Boundary at Mt. Chopaka ridge, following a broad U-shaped trough which 

 continues southwardly to and beyond Loomis, Wash. Two miles north of 

 Palmer lake (see Chopaka Quadrangle of the United States Geological Survey 

 Atlas), the river abruptly leaves the trough and crosses Kruger Mountain 

 plateau in a deep canyon which also carries the branch of the Great Northern 

 railway on its low grade up the river. The forms of the valleys and the course 

 of the river have been affected by the activities of the late Pleistocene local 

 glaciers. An account of this and other important diversions of principal Cor- 

 dilleran rivers by Glacial activities is given in a remarkably suggestive, all too 

 brief, paper by Willis.* 



Throughout the whole hundred-mile section, well-developed glacial cirques 

 are entirely wanting. The field evidence is clear that apart from the few large 

 valley glaciers already noted, there were very few local sheets to survive the 

 ice-cap as it finally disappeared from the mountains. 



Okanagan Range. 



The western edge of the ice-cap at the Forty-ninth Parallel was situated 

 in the Okanagan range, from twenty-five to thirty-five miles west of the Simil- 

 kameen river. Many accordant observations showed that on the slopes of the 

 ridge bearing Cathedral Peak and Park mountain, the upper limit of the ice 



* B. Willis, Bulletin 40, U.S. Geol. Survey, 1887. Cf . W. L. Dawson on ' Glacial 

 Phenomena in Okanagan County, Washington/ American Geologist, Vol. 22, 1898, p. 203. 



