362 THE GREAT ICE AGE 



than anything else I saw in the Alps, with the exception of 

 some recent avalanches, I jotted down what appeared to me 

 to be the most important points of difference. They stand 

 thus : 



1. Glaciers heap up their debris in abrupt ridges. Floating 

 ice sometimes does this, but more usually spreads its load in a 

 more or less uniform sheet. 1 



2. The material of moraines is all local. Floating ice carries 

 its deposits often to great distances from their sources. 



3. The stones carried by glaciers are mostly angular, except 

 where they have been acted on by torrents. Those moved by 

 floating ice are more often rounded, being acted on by the 

 waves and by the abrading action of sand drifted by cur- 

 rents. 



4. In the marine glacial deposits mud is mixed with stones 

 and boulders. In the case of land glaciers, most of this mud 

 is carried off by streams and deposited elsewhere. 



5. The deposits from floating ice may contain marine shells. 

 Those of glaciers cannot, except where, as in Greenland and 

 Spitzbergen, glaciers push their moraines out into the sea. 



6. It is of the nature of glaciers to flow in the deepest 

 ravines they can find, and such ravines drain the ice of exten- 

 sive areas of mountain land. Floating ice, on the contrary, acts 

 with greatest ease on flat surfaces or slight elevations in the sea 

 bottom. 



7. Glaciers must descend slopes and must be backed by 

 large supplies of perennial snow. Floating ice acts indepen- 

 dently, and being water-borne may work up slopes and on 

 level surfaces. 



8. Glaciers striate the sides and bottoms of their ravines 

 very unequally, acting with great force and effect only on 

 those places where their weight impinges most heavily. Float- 



1 Under floating ice I include floe, pack, and bordage ice as well as 

 bergs. 



