244 The American Geologist. October, 1902. 
Certain it is that the adjacent mountains are worn away, 
and the material is continually carried forward, and finally 
dropped, for the most part, at the end of the glacier in the 
form of terminal moraines. The mass of general evidence 
goes to show also that the amount of englacial debris oi' 
an Alpine glacier is, with few exceptions, relatively small com- 
pared with that moving upon and with the surface of the ice- 
mass. 
This superficial morainic material divides itself in the case 
of Alpine glaciers, as is well known, into three classes : the 
lateral moraines ; medial moraines ; and terminal moraines. In 
the Polar ice-sheet another type of much importance is known 
as ground moraines. Lateral moraines result from the 
weathered material of the adjacent mountains falling upon the 
ice-mass, and distributing itself along the edges of the glacier. 
Wherever two tributary glaciers combine, it is readily seen 
that one lateral of each will combine with the other to form a 
medial moraine. 
The lateral and medial moraines seem to be particularly 
important onh^ in so far as they bear upon the disintegration 
of the mountains, and thus act as powerful abrasive and 
erosive agents, and possibly influence somewhat also the rate of 
flow of the glacier. 
In some glaciers of the Piedmont type, however, the lateral 
moraines are of some moment. As a typical example the 
Malaspina glacier, previously referred to. is interesting. This 
plateau of ice about 1,500 feet high, is free from medial 
moraines, though broken over its surface by thousands of 
small crevasses. Moraines cover the border, however, and ac- 
cording to Russell, * they are all formed of the debris 
brought out of the mountains by the tributary Alpine glaciers, 
and concentrated at the surface by reason of the ablation of 
the ice. Some of the outer portions of the fringing moraines 
are covered with vegetation. Trees of cottonwood, alder, 
shrubs and ferns grow so densely as to prevent passage through 
them ; and all on ice which in many places is not less than one 
thousand feet thick. 
The classes of moraines that are of most importance are the 
terminal, and so-called ground moraines. A rather sharp 
*I. C. Russell. Am. Jour, of Science. Vol. 143, 1S92. 
