2 GEORGE V. SESSIONAL PAPER No. 25a A. 1912 



CHAPTER XXI. 



GLACIATION OF THE CORDILLERA AT THE FORTY-NINTH 



PARALLEL. 



Introduction. 



While collecting the data on the problems of bed-rock geology 

 the writer attempted to note the leading observations which could be made 

 on the Pleistocene glaciation of the Boundary belt. The results lack much in 

 completeness, but they have the value of corroborating the general views of Daw- 

 son and other pioneer geologists who have traversed this part of the mountain 

 chain. The study has further indicated how great a field is awaiting the 

 detailed attention of glacial experts. The results of the writer's reconnaissance 

 along the transmontane section will be summarized in the present chapter. 

 Meagre as they are in certain respects, they have been achieved only after 

 hundreds of more or less arduous climbs had been made; it is thought that 

 . a quantitative statement of the principal facts may be of some service to the 

 students of the vast glaciated tract of the Cordillera. 



A preliminary understanding of the principal conclusions concerning the 

 distribution of the Pleistocene ice-fields can be attained by a glance at the 

 diagrammatic section of Plate 49. It will be observed that the section shows 

 a high degree of symmetry. The middle part of the Cordillera, 300 miles in 

 width, was covered by a continuous ice-cap. To east and to west of this cap 

 the Rocky Mountain system and Cascade mountain system were respectively 

 covered by three sets of valley glaciers. 



The eastern slope of the Clarke range shed ice-streams to the piedmont 

 sheet at the Great Plains. The western slope of that range and the eastern 

 slope of the MacDonald range shed valley glaciers to the main, south-flowing 

 trunk glacier in the Flathead valley. The eastern ice-shed of the central ice-cap 

 was located on the high ridges of the MacDonald range. 



Similarly, the western slope of the Skagit range shed many valley glaciers 

 to the piedmont sheet of the Gulf of Georgia, while the eastern slope and the 

 Hozomeen range fed the local sheets which met and were drained away south- 

 ward, down the Skagit valley. 



A few nunataks projected above the ice-cap. In general the erosion of 

 this colossal sheet tended to soften the contours of the overridden moun- 

 tains, rounding off the corners, much as the sharp peaks and angles of the 

 Greenland and Labrador coasts have been affected by the eastern ice-caps. In 

 the belts of valley-glaciers, on the other hand, glacial erosion has greatly 



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