36 THE AMERICAN NATURALIST. 
great numbers and are popularly known as “ Giants’ Kettles.” 
In Oswald Heer's Urwelt der Schweiz we find a full description 
of some of the Swiss pot-holes. On the mode of formation of 
these holes Geikie speaks as follows: ** Among the Alps, during 
the day in summer, much ice is melted and the water courses 
from the glaciers accumulate in brooks which, as they reach the 
crevasses, tumble down in rushing waterfalls, and are lost in the 
depths of the ice. Directed, however, by the form of the ice 
passage against the rocky floor of the valley, the water descends 
at a particular spot, carrying with it the sand, mud, and stones 
which it may have swept away from the surface of the glacier. 
By means of these materials it erodes deep pot-holes in the solid 
rock, in which the rounded detritus is left as the crevasse closes 
up or moves down the valley." 
