314 THE BEAUTIES OF NATURE chap. 



shallow. Some geologists, Geikie, for in- 

 stance, ascribe them to the fact of these 

 regions having been covered by sheets of 

 ice which strewed the land with irregular 

 masses of clay, gravel, and sand, lying on a 

 stratum impervious to water, either of hard 

 rock such as granite or gneiss, or of clay, so 

 that the rain cannot percolate through it, and 

 without sufficient inclination to throw it off. 



2. To Ramsay's second class of Lakes 

 belong those formed by moraines. The 

 materials forming moraines being, however, 

 comparatively loose, are easily cut through 

 by streams. There are in Switzerland many 

 cases of valleys crossed by old moraines, but 

 they have generally been long ago worn 

 through by the rivers. 



3. Ramsay and Tyndall attribute most of 

 the great Swiss and Italian lakes to the action 

 of glaciers, and regard them as rock basins. 

 It is of course obvious that rivers cannot 

 make basin-shaped hollows surrounded by 

 rock on all sides. The Lake of Geneva, 

 1230 feet above the sea, is over 1000 feet 

 deep ; the Lake of Brienz is 1850 feet above 



