civ GENERAL SUMxAIARY OF SCIENTIFIC AND 



subject by showing, as the result of long studies of Alpine glaciers, 

 that the plasticity of ice is such that it flows like a river over and 

 around obstacles instead of sweeping them away. An Alpine glacier 

 advancing over a tolerably level surface overrides the loose material 

 in front, scarcely disturbing it, and the great retreating glaciers 

 leave behind them nothing like the boulder-clay or ground moraine ; 

 the detrital matter from them, which is small in amount, being, like 

 that of the terminal moraines, derived from the surface of the glacier. 

 He argues that the glaciers, though they have moulded surfaces, have 

 not excavated nor modified the features of the valleys, which are an- 

 terior to the glaciers, and are due to fluviatile agencies. There are 

 phenomena of surface -geology for which the hypothesis of great 

 glaciers oflFers a plausible solution; but it must be received with 

 many limitations, w^hile the objections which are urged against it are 

 such that the present attitude of many judicial minds is at least one 

 of doubt. 



