21 



Alberta, three glacial provinces stand out in bold relief 

 as shown in the accompanying cut. The middle part 

 of the Cordillera was covered by a continuous ice-cap. 

 To the east of this cap, the Alpine belt which includes 

 the greater part of the Rocky Mountain, Purcell, Selkirk 

 and Columbia systems, was covered by numerous valley 

 glaciers whose direction of flow was regulated in the main 

 by the great master longitudinal valleys. Similarly in 

 the Alpine belt lying to the west of the Interior Plateau 

 region, the direction of the ice drainage was governed 

 by the main depressions in that belt. The continental 

 ice-cap of the Interior Plateau region in Southern British 

 Columbia moved in general in a southerly direction. 



PHYSIOGRAPHIC HISTORY. 



Foundation for the construction of the present form of 

 the Cordillera was laid at the closing of the Cretaceous 

 period, when the last general orogenic revolution in the 

 Cordillera took place. Mild deformation of the Eocene 

 Oligocene and Miocene formations substantiates the date 

 of this general deformation. The resultant topography 

 superimposed upon a terrane composed of quartzites, 

 hard schists, massive limestones and dolomites, and granites 

 was one of high relief and intricate design. The work of 

 reducing the original chain of early Eocene mountains to 

 the present more subdued relief is of the same order as 

 that accomplished by the erosion of the entire Tertiary 

 period in equally resistant terranes of the Appalachians. 

 The development of the Rocky Mountain and Purcell 

 trenches, the Selkirk and Okanagan valleys, forms a series 

 of tasks comparable to those of opening the Hudson and 

 Connecticut valleys in the east. The many narrow 

 valleys of the Cordillera are analogues of the young to 

 mature Tertiary valleys cut in the Cretaceous peneplain 

 of the Appalachians. During late Tertiary there was 

 an important uplift in the Cordilleran region claimed by 

 Dawson to reach 2,000 feet for the Interior Plateau region. 

 This late Tertiary uplift invigorated the rivers; it did 

 not begin a new erosion cycle at the close of a completed 

 former cycle ; hence the entire post-Laramie history belongs 

 to one complex erosion cycle. 



