REPORT OF TEE CHIEF ASTRONOMER 583 



SESSIONAL PAPER No. 25a 



velocity of the local ice. An inspection of Eeid's map of Muir glacier shows 

 the exceeding importance of concentration of flow in explaining the wonderful 

 stream of rock-flour always pouring out from that ice-sheet. The lowering of 

 its bed by three-fourths inch per year is progressing at a rate amply sufficient 

 to account for fiord-excavation on the largest scale. 



The prodigious erosion of the Front ranges necessarily involved the car- 

 riage of hundreds, if not thousands of cubic miles of rock-debris to lower 

 ground. On the east, the drift from the Clarke range was first transferred to 

 the piedmont ice-sheets and was then slowly spread over a wide belt on the 

 Great Plains, seldom attaining phenomenal thickness at any point. The 

 detritus carried down the western valleys entered the relatively restricted Flat- 

 head trough where even the great North Flathead glacier was incompetent to 

 handle all of the vast load of rock-matter. In consequence, the eastern side of 

 the Flathead trough is covered with many huge moraines which are winged out 

 from the spurs of the Clarke range. The glaciers which occupied the valleys 

 of Kishenehn, Starvation, and Kintla creeks built such moraines, from three 

 to four miles in length, and from 1,000 to 1,500 feet in height. Others of 

 similar dimensions were formed from the drift of glaciers occupying the valleys 

 of Bowman creek, Quartz creek, and Logging creek, south of the Line. Nearly 

 all of these great drift accumulations are mapped in the Kintla Lakes Quad- 

 rangle of the United States Geological Survey atlas. 



At first the writer was sceptical as to the simple morainal origin of these 

 ridges, but a long search for bed-rock outcrops, attended with entirely negative 

 results, and the general topographic relations of the ridges left little ground 

 for doubt that practically the whole of each ridge is composed of drift. Most 

 of this drift seems to have been, in each case,' derived from the adjacent canyons. 

 Boulders of the Siyeh limestone and of the Purcell Lava formation — two 

 prominent constituents of the Clarke range — are very abundant in the drift. 



In their lower parts, Kishenehn, Starvation, and Kintla creeks are flowing 

 through the troughs occupied by the corresponding glaciers in their latest 

 stages. These troughs are in fact, the little altered casts of the glaciers as 

 they debouched from the mountains into the Flathead valley. (Plate 52.) The 

 affluent glaciers with the intervening moraines were deflected down the main 

 valley by the southward-moving North Flathead glacier. The moraines are 

 thus systematically directed in southwest directions from the mountain spurs 

 (see Plates 12 and 52, and the Kintla Lakes Quadrangle sheet). 



The -North Flathead glacier at its maximum stage was from nine to twelve 

 miles in width, and at the Forty-ninth Parallel from 1,500 to 2,000 feet in 

 greatest depth. The highest point at which exotic boulders were found occurs 

 on the 5,100-foot contour on the west side of the valley. It is probable, how- 

 ever, that the glacier at one time covered the mountain slopes to the 5,500-foot 

 contour and perhaps as high as the 6,000-foot contour. The river is 4,000 feet 

 above sea at the Boundary Line. 



On the western side of the valley there are no such systematic moraines 

 as those just described on the eastern side. The main glacier was able to 

 remove most of the debris fed to it by the glaciers affluent from the MacDonald, 



