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 
