CHAPTER XXII. 



WATER AND ICE. 



We now have entered upon a subject that 

 is of intense interest, studied from the stand- 

 point of facts as they exist to-day and of his- 

 tory as we read it in the rocks and bowlders 

 that we find distributed over the face of the 

 earth. 



The whole northern part of the United 

 States extending to a point south of Cin- 

 cinnati was at one time covered with a great 

 ice-sheet, traces of which are plainly visible 

 to anyone who has made anything of a study 

 of this subject. The glaciers now to be seen 

 in British Columbia and Alaska, great as they 

 seem to one viewing them to-day, are by com- 

 parison with what once existed simply micro- 

 scopic specks of ice. Glaciers, like rivers, flow 

 by gravity, following the lowest bed and lines 

 of least resistance; the difference being that 

 in the one case the flow is rapid, while in the 

 other it is scarcely visible, except by measure- 

 ment from day to day. Before entering upon 

 a description of the law that governs the flow 

 of glaciers, let us stop and give a little 

 m 



