578 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



sharpened the mountain summits and ridges. This latter effect has been due 

 chiefly to head-wall recession of the upper ends of the local glaciers. The 

 amphitheatres or cirques, which are related products, will receive some illustra- 

 tion, and certain points in the theory of their formation will be discussed. Other 

 cirques were developed in the area of the ice-cap, either about the projecting 

 mmataks, or, and more generally, during the later time when the ice-cap, through 

 climatic wastage, had become broken up into local areas of snow-field and 

 valley glaciers. 



Special attention was paid by the writer to the determination of the upper 

 limits of the ice-sheets in the different ranges. The familiar criteria were used, 

 and, for each glacial province, gave accordant results. The position and origin 

 of high-level erratics, the extent of glacial polishing and grooving, the directions 

 of striae on the higher peaks and ridge, — in general, the distinguishing of 

 regional from local glaciation, were the natural points to be observed in mapping 

 the limits of the ice-cap in altitude and in longitude. The errors in altitude 

 are in most cases believed not to exceed one hundred or two hundred feet. In 

 certain cases the striae did not give sure evidence as to the direction in which 

 the ice had moved. In such cases lunoid furrows could sometimes decide the 

 question, the direction of movement being always in the sense of the furrow's 

 convexity. It may be noted in passing that lunoid furrows are relatively rare 

 on the Cordilleran ledges as compared with the multitudes which may be seen 

 along the Labrador coast. The reason for thig contrast in the two heavily 

 glaciated regions is not apparent. 



The glacial deposits are as a rule of quite normal composition but rarely 

 show systematic types of form. A few such forms will, however, be noted in 

 describing the great master valleys, which in Glacial times were occupied by 

 huge trunk glaciers either independent of, or inherited from, the central 

 ice-cap. 



The curious relation of the Rocky Mountain piedmont glaciers to the 

 Keewatin ice-cap was not directly studied. For information relating thereto 

 the reader is referred to Dawson's glacial papers* and to Calhoun's more recent 

 paper on ' The Mountain Lobe of the Keewatin Ice Sheet 'f 



In what follows it will be seen how closely the writer's results accord with 

 the general conclusions arrived at by Dawson.:}: 



The central ice-cap broke up into several wide lobes at no great distances 

 south of the Forty-ninth Parallel. Within the Boundary belt no indication 

 that there was more than one Glacial epoch in the Pleistocene was found in any 

 one of the six field-seasons devoted to the section. All observed drift had the 

 same freshness as that laid down in the later Wisconsin epoch of eastern 

 glaciation. 



* Especially that in the Report of Progress, Geol. Surv. of Canada, 1882-4, Pt. C, 

 p. 139. 



tF. H. H. Calhoun, Prof. Paper, No. 50, U.S. Geol. Surv., 1906. 

 t See G. M. Dawson, Trans. Roy. Sc ;., Canada, Vol. 9, 1891, p. 3. 



