SOME LOCAL DETAILS. 153 



Auierican plateau as far as the middle states of the Union, 

 or to the lines of the modern Ohio and Missouri rivers. 



4. The region of Manitol)a and the North-west. This 

 constitutes another, and now more elevated, plain, con- 

 tinuous with the former and with the great American 

 plateau on the soutli, and extending north-west to the 

 Arctic sea. It has the Laurentian axis on the north-east, 

 and the Rocky mountains, the eastern ridges of the great 

 Cordillera of the Pacitic coast on the west. In the early 

 Pleistocene, this great plain was at a lower level than at 

 present, and the ico and ih'brk from the Laurentide and 

 Cordilleran glaciers, and more especially from tlie former, 

 were distributed by water over its surface. In the mid- 

 glacial age it was partially elevated and overspread with 

 vegetation, but in the later glacial age it was much more 

 extensively submerged and its waters covered witii float- 

 ing ice. 



5. The great Cordilleran region of the west, embracing 

 the Eocky mountains, the Crold aiul Selkirk ranges, the 

 elevated interior plateau (jf JU'itish (Jolunibia, and the 

 coast ranges of tlie Tacific. In the early glacial period 

 tliis region seems to have stooil high out of the waters 

 which extended to the east and west of it, and was covered 

 with a great neve, or snow-cap, sending off gigantic 

 glaciers in all directions, but more es[)ecially to the south, 

 north, and west. In the mid-glacial period it was greatly 

 retluced in height, and, for the most part, denuded of ice, 

 which, however, returned to it in diminished force in the 

 second or later glacial age. 



Lastly : Canada includes a portion of the Arctic basin 

 north of the Laurentian ranges, and partly enclosed in 

 the wide angle which they form northward. This, so far 

 as known, was, througiiout the glacial age, at a low level. 



