APPEARANCES OF GLACIERS AND SNOW-FIELDS. 167 
ing its channel, eroding valleys, often covering vast areas, 
an agent of great destructive power. 
‘The motion of a glacier being largely due to expansion 
from the consequences of its melting, is slower at night 
than during the day, and in winter than in summer; the 
movement is greater in the middle, than on the sides, 
where it is held in check by friction, and also more slug- 
gish at the bottom than atthe top. A glacier will accom- 
modate itself to the sinuosities and unevenness of its bed, 
expanding or contracting like the waters of a river, and 
will precipitate itself over a ledge, making a cascade of 
ice: these I have seen in almost every glacier in Norway. 
The ice is often broken transversely, the moraines are 
engulphed in the crevasses and lost. ‘The main glacial 
stream starts with a moraine on each side ; long dark bands 
raised above the ice are formed by the stones and earth 
which have fallen down the side of the mountain, in the 
same manner‘as the heaps of stones and débris we find at 
the base of mountains, and in many ravines and valleys. 
These lateral or marginal moraines vary in height accord- 
ing to the amount of the deposits massed together, and to 
the time of their formation ; they range from a few feet to 
twenty feet in heignt, but are never much more, for there 
is no time for accumulation ; the material is collected as 
the ice moves downward, and the motion of the Norwegian 
glacier may be a few hundred feet a year. These moraines 
stand in regular ridges, and are slowly and surely carried 
to the end of the glacier; their origin, by the materials, 
can often be traced back for great distances. As the 
frozen river moves onward, it is joined by others, all uniting 
in one solid mass; the moraines meet side by side, and 
remain distinct on the journey down. The number of 
these moraines indicates how many branch streams have 
united with the main trunk. Sometimes a glacier is com- 
pelled to make its way through a narrow defile; then the 
mass of ice contracts, and becomes deeper, and a grinding 
process takes place on the sides and at the base with im- 
mense force; many valleys with perpendicular walls have 
