II 2 
SCENERY OF SWITZERLAND. 
rapidly than a small one. Many bodies will in small 
dimensions retain their form, which in larger masses 
would be unable to support their own weight. A 
small clay figure will stand where a life-sized model 
will require support. Sealing-wax breaks under ten- 
sion like ice, but under even slight pressure gradually 
modifies its form. 
Prof. Heim is convinced that if a mass of lead, 
corresponding to a glacier, could be placed in a Swiss 
valley, it would move to a great extent like a glacier. 
The size of a glacier is therefore an important factor 
in the question, and throws light on the more rapid 
movement of the greater glaciers, even when the in- 
clination of the bed is but slight. In Heim’s opinion 
then the weight of the ice is sufficient to account for 
movement, though the character of the movement 
and the condition of the glacier is due to fracture 
and regelation. He sums it up in the statement 
that gravity is the moving force, and the glacier 
grains the prevailing mechanical units of movement. 
Crevasses. 
The rigidity of ice is well shown by the exist- 
ence of crevasses. They may be divided into three 
classes: — 
