34 



THE ICE AGE IN CANADA. 



Cordilleran 

 Cordilleran zone at a high eleva- 

 tion. Period of most severe glaei- 

 ation and maximum development 

 of the great Cordilleran glacier. 



SCHEME OF CORRELATION OF THE PHENOMENA OF THE GLACIAL 

 PERIOD IN THE CORDILLERAN REGION AND THE REGION OF 

 THE GREAT PLAINS (IN ASCENDING ORDER). 



Region of the Great Plains. 



Correlative subsidence and sub- 

 mergence of the great plains, 

 with possible contemporaneous 

 increased elevation of the Lauren- 

 tian axis and maximum develop- 

 ment of ice upon it. Deposition 

 of the lower boulder clay of the 

 plains. 



Correlative elevation of the 

 western part of the great plains, 

 which was probably more or less 

 irregular, and led to the produc- 

 tion of extensive lakes, in which 

 inter-glacial deposits, including 

 peat, were formed. 



Gradual subsidence of the Cor- 

 dilleran region and decay of the 

 great glacier, with deposition of 

 the boulder clay of the Interior 

 Plateau and the Yukon Basin, of 

 the lower boulder clay of the 

 littoral, and also at a later stage 

 (and with greater submergence) of 

 the inter-glacial silty beds of the 

 same region. 



Re-elevation of the Cordilleran 

 region to a level probably as high 

 as or somewhat higher than the 

 present. Maximum of second 

 period of glaciation. 



Partial subsidence of the Cor- 

 dilleran region to a level about 

 2,500 feet lower than the present. 

 Long stage of stability, during 

 which the white silts were laid 

 down. Glaciers of the second 

 period considerably reduced. Up- 

 per boulder clay of the coast 



Correlative subsidence of the 

 plains, which (at least in the 

 western part of the region) ex- 

 ceeded the first subsidence and 

 extended submergence to the base . 

 of the Rocky Mountains near the 

 forty -ninth parallel. Formation of 

 second boulder clay, and (at a 

 later stage) dispersion of large 

 erratics. 



Correlative elevation of the 

 plains, or at least of their western 

 portion, resulting in a condition 

 of equilibrium as between the 

 plains and the Cordillera, their 

 relative levels becoming nearly as 

 at present. Probable formation 

 of the Missouri Coteau along a 



