584 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



range. Those glaciers were not so long nor so efficient in developing cirques 

 as the glaciers draining the Clarke range. The drift material carried to the 

 North Flathead glacier from the western range was therefore very much less 

 abundant than that issuing from the eastern range. When the main glacier 

 finally wasted away the new relief of the Flathead valley was unsymmetric, so 

 that the constructional path of the river was located, as at present, on the 

 western side of the wide trough. 



. Galton-MacDonald Mountain Group. 



The rugged topography of the Galton and MacDonald ranges has been 

 largely shaped by local cirque-glaciers. There is plenty of evidence, however, 

 that at the time of maximum glaciation these local sheets were confluent. From 

 the western ridge of the MacDonald range the flooded cirque-glaciers formed a 

 mass of ice continuous with that which then covered the Purcell range and the 

 ranges further west. The erosive effects of the ice-cap have been greatly 

 masked by those of the numerous local glaciers which persisted, long after the 

 surface of the general ice-flood had, by wasting, been lowered from its highest 

 levels. Somewhat prolonged search was therefore required before undoubted 

 evidence of the upper limit of the ice-cap could be obtained in these ranges. The 

 search was necessarily confined to the tops of the ridges dividing the cirques. 



The most favourable locality discovered is that of the long meridional ridge 

 running south from the Boundary slash at 114° 48' W. Long. On that ridge 

 at the 7,000-foot contour, distinct grooves and strias were found. These belonged 

 to two different sets, one trending S. 20° E.; the other S. 80° W. In both 

 cases the ice movement was independent of the axes of the flanking cirques. 

 The whole ridge was overrun by ice which, at different times, flowed southward 

 and westward. 



A study of the peaks and ridges reaching heights of 7,500 feet or more 

 showed that erratic material was not to be found above the 7,300-foot contour, 

 above which also the other familiar evidences of general glaciation were 

 absent. The writer has concluded that the 7,300- foot contour marks quite closely 

 the average surface-level of the ice-cap in the Galton range and western part 

 of the MacDonald range. 



Using the same criteria, it was observed that the ice-cap was limited by the 

 ridge overlooking the Wigwam river on the east. East of that ridge the glacia- 

 tion seems to have been entirely local, the many cirques draining into the 

 great North Flathead glacier. The latter glacier seems, at its maximum, not 

 to have reached higher than the 6,000-foot contour. Its surface was, therefore, 

 some 1,800 feet lower than that of the ice-cap eight or ten miles distant. Down 

 this steep descent transverse ice streams, flowing out from the ice-cap, helped to 

 feed the North Flathead glacier. 



The troughs of the transverse glaciers were later occupied by torrential water 

 derived from the greater ice-masses as these melted. Such an old spill-way is 

 represented in the box-canyon crossing the MacDonald range at the Boundary 

 line. The canyon is now almost dry, but its bed is abundantly supplied with 

 pot-holes and other evidences of heavy scouring by a rapid stream of water. 



