388 HISTORICAL GEOLOGY. 



dian highlands the material has heen carried southeast- 

 ward, southward, and southwestward. The distance car- 

 ried has heen in some cases several hundred miles. 



Bed-Bock Surface. Wherever the drift-mantle is 

 removed, the hed-rock underlying is found to be glaciated., 

 i. e., it presents a smooth, billowy surface, scored with 

 straight parallel marks, precisely like the pathway of a 

 glacier, described on page 61. The general direction of 

 these marks is the same as that of the transport of the 

 bowlders, viz., southeast, south, and southwest. 



Southern Limit of the Drift ; Ice-Sheet Moraine. 

 The most characteristic of the phenomena described, 

 viz., the stony clay, the glaciated bed-rock, and the great 

 bowlders, extend over the whole northern portion of the 

 continent, down to about 38 to 40 north latitude. 

 Along this southern limit are found remnants of the 

 terminal moraine of the ice-sheet. 



Its position is marked on the map by the strong line. 

 Within this, and marked on the map by the dotted lines, 

 another and later and far distincter terminal moraine is 

 seen sweeping about the Great Lakes and westward in 

 huge festoons (Fig. 347). 



Explanation. The simplest explanation of these facts 

 is, that during this epoch the whole northern part of the 

 continent was elevated, so that the Canadian highlands 

 were 1,000 to 2,000 feet above its present level, and com- 

 pletely covered with an ice-mantle several thousand feet 

 thick, as Greenland and the Antarctic Continent are to- 

 day. This ice-mantle, covering everything except per- 

 haps the highest peaks, moved southeastward, southward, 

 and southwestward, scoring the whole surface of the coun- 

 try in its path, and accumulating bowlders and earth be- 

 neath it. At its limit, represented by the strong line seen 

 on the map, the accumulations, being more abundant, 

 formed a moraine. After a while, the ice-limit, by melt- 

 ing, went northward, dropping bowlders in its course to 



