REPORT OF THE CHIEF ASTRONOMER 595 



SESSIONAL PAPER No. 25a 



rival the Skagit range for ruggedness. This property, especially as relates to 

 the steepness of slopes, the prevalence of knife-edges, ridges, and sharp horns," 

 is in part the result of prolonged erosion by Pleistocene local glaciers. The 

 descendants of those glaciers are represented by numerous small sheets occupy- 

 ing the northerly slopes of the higher massifs from Glacier Peak to Tamihy 

 mountain. In Glacial times the incomparably vaster rivers of ice must have 

 headed at about the same levels as the existing glacierlets, that is above the 

 7,000-f oot contour. From those -heads to the sealevel the average descent on 

 the west slope was from 200 to 400 feet to the mile. At the maximum 

 glaciation the master glaciers of that slope had depths from 4,000 to 5,000 

 feet. These colossal bodies moving on gradients of over 100 feet to the mile 

 were plainly competent to perform rapid geological work. There is little 

 wonder that the longest of the sheets occurring in the Boundary belt — the 

 ^hilliwack glacier — has produced a long, continuous U-shaped trough, fiord-like 

 in its cross-section. Such is the character of the Chilliwack valley from the 

 head of the lake to the debouchure thirty miles below. The intensity of the 

 Glacial erosion is shown by the fact that the mountain spurs which in rhythmi- 

 cal alternation overlooked the pre-Glacial valley to right and left, have been 

 truncated on a large scale (Plate 59). In evident fashion, though in less 

 degree, the effluent glaciers occupying the valleys of Depot, Silver, Middle, 

 Slesse, and Tamihy creeks, have similarly driven back the lateral spurs, greatly 

 steepened the valley walls, and reduced intervening ridges to razor-back profiles 

 for miles together. Above the ridges tower the pinnacles like Sleese mountain, 

 Tamihy mountain, Glacier Peak, and many others which lend their grandeur to 

 the panoramas visible from elevated stations. Just below the summits glacial 

 amphitheatres lend not inferior variety of relief to the rugged range. Tandem 

 cirques, sometimes holding picturesque lakelets in each, are here, as in the 

 Selkirk and Clarke ranges, not uncommon. 



Chilliwack lake, one of the most beautiful in the Cordillera, is held at its 

 level of about 2,000 feet above sea by a strong boulder moraine, which in a 

 smooth, graceful curve of 2,000 yards loops across the valley bottom. (Plates 

 58 and 60). As shown by soundings in the lake (265 feet deep, 300 yards off 

 shore from the middle of the moraine), the moraine seems to be at least 350 

 feet high. Owing to lack of sounding-line the maximum depth of the lake 

 was not determined. Two thousand yards below the delta at the upper end of 

 the lake, the depth in the middle was measured at 198 feet. The boulder 

 deposit is continuous for more than a mile down the valley, descending by two 

 remarkably regular steps about 150 feet in that distance. The boulders are of 

 all sizes up to those thirty feet long and fifteen feet thick, growing generally 

 smaller down the valley. Almost all of them are composed of the same granite 

 which surrounds and underlies the lake. The moraine was evidently formed 

 during a long halt in the recession of the Chilliwack glacier. At the outlet a 

 75-foot notch has been cut through the moraine. Thence the Chilliwack river, 

 on a gradient of nearly 100 feet to the mile, rushes on its torrential way to the 

 Fraser flats. 



25a— vol. iii— 39 



