EVIDENCE FKOM THE CASCADES 39 



Cascades. — A very recent paper by Willis * revives the interesting ques- 

 tion of the origin of lake Chelan, favoring the suggestion! of ice erosion. 



The problem of the Chelan basin is practically the same as that of 

 other deep lakes, like the Swiss lakes, found in the tracks of former 

 stream glaciers, J and it is well to discuss it here at sufficient length. 

 The descriptions following are from Willis' paper: 



" Lake Chelan is a slender body of water, 65 miles long, whose southeastern end 

 lies open to the sky between the grass-grown hills of the outer Columbia valley, 

 while its northwestern lies in shadow between precipitous mountains in the heart 

 of the Cascade range. . . . The canyon is that of the Stehekin-Chelan river, 

 which rises in latitude 48° 30 / in glaciers of the Cascade range at altitudes of 5,000 

 to 8,000 feet. The headwaters descend very abruptly, 1,000 to 1,800 feet in the 

 first mile below the glaciers, and combine in a U-shaped valley of gentler grade, 

 the fall being 2,500 feet in 23 miles. This section is cut in rock bottom. For 12 

 miles farther down stream the valley is floored with boulders, coarse gravel, and 

 sand, and the slope is but 20 feet to the mile, ending in the delta which the stream 

 is building into lake Chelan. 



" The gravel-filled section of the valley is no doubt deeply cut in the solid rock* 

 since but a short distance beyond the front of the delta the lake is more than 500 

 feet deep. For a distance of 35 miles the depth varies from 1,000 to 1,400 feet, 

 1,419 being the maximum yet sounded. As the water surface is but 1,079 feet 

 above sea, the bottom of the lake is for a short stretch 300 feet below sealevel, and 

 an interesting question is raised as to how so deep a basin originated. Fifteen 

 miles from its outlet the lake begins to shallow, and in its lower reach does not 

 exceed 200 feet in depth." (Page 58.) 



11 Lake Chelan occupies a canyon in granite and gneissoid rocks. The waters 

 are retained by a dam of drift, but discharge through the gorge of Chelan river 

 into the Columbia, whose bed is not far from solid rock. According to the alti- 

 tudes above sea of rock in place in the Columbia, several miles below the junction, 

 that of the lowest rock sill over which the waters of lake Chelan can have escaped 

 is about 700 feet. . . . The maximum sounding was 1,419 feet — i. e., to 340 feet 

 below sealevel, or 1,040 feet below the rock rim of the basin." (Page 81.) 



" Effects of glacial erosion are obvious throughout the Chelan-Stehekin system. 

 They may be traced from the moraines of existing glaciers, in the cirques about 

 the headwaters, down the grooved and rounded canyon walls, into the waters of 

 lake Chelan, and out to the terminal moraine near the Columbia, in all a distance 

 of 70 miles. Three miles above the terminus of the ancient glacier its thickness 

 was 1,000 feet, and its surface stood about this amount above the present level of 

 lake Chelan. Thirty miles above its lower end, that is, near Safety Harbor creek, 

 the thickness of the ice was 4,500 feet, and toward the head of the lake it probably 

 exceeded 5,000 feet. " ( Page 82. ) 



"... The walls of the canyon are sloping, not precipitous. . . . The 



* Bailey Willis: Physiography and deformation of the Wenatchee-Chelan district, Cascade 

 range. U. S. Geol. Survey, Profes. Paper No. 19, 1903, pp. 41-97. 



f Henry Gannett : Lake Chelan. Nat. Geog. Mag., vol. ix, pp. 417-428, 1898. 



X The New York or Finger lakes are an entirely different problem, as their valleys were never 

 occupied by stream glaciers, but only by lobes of the continental glacier in valleys sloping toward 

 the ice (see discussion, pages 55-73). 



