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established. The rate at which the glacier moves, depends 
on the angle of the slope on which it rests, or the width of 
its channel, and on its own depth. As the two first conditions 
change from the progress of the glacier, the last continually 
alters, the glacier thus undergoing the diversities to be found 
in a river — massing itself in the gorges and moving like rapids, 
or spreading itself out in the plains, where it stagnates into 
water, or sluggishly creeps along. 
This enables us to understand the analogy that has so often 
been suggested between a glacier and a river. The comparison 
is in every respect true, for the glacier is fed by tributaries, 
bends round a corner, accommodates itself to the shape and 
size of its channel, and is retarded by the friction it encounters 
against its bed. In fig. 1, four glaciers are seen to pour into 
a single channel, where they are welded into the Mer-de- 
Glace. The channel through which the united mass is urged, 
is seen to be extremely narrow. Professor Tyndall has deter- 
mined the width of the three main tributaries just before their 
point of junction. They are as follows : 
Glacier du. Geant . . . 
Glacier du Lechaud 
Glacier du Talefre ... 
1134 yards 
825 „ 
638 „ 
* Making a total of 
2597 
At Trelaporte the united stream was measured, and found 
to be a channel only 893 yards wide.* Eight through this 
narrow gateway the entire quantity of ice, which was pre- 
viously contained in a bed nearly three times as wide, is con- 
tinually being forced. This fact is surely one of the most im- 
pressive in the whole of glacial phenomena. It reveals at once 
the enormous pressure to which the glacier must be subject, in 
order to thrust a solid body like ice through such a gorge. 
But it is only the shape of the glacier which changes ; its 
volume is not materially affected by this compression. Just 
as would occur with a river similarly circumstanced, the depth 
and velocity of the trunk glacier at Trelaporte becomes greater 
than before existed in any of its tributaries. 
The union of several glaciers is marked by the transference 
of a corresponding number of moraines, minus one , from the 
sides to the centre of the glacier. In other words, at the 
junction of every two glaciers, two lateral moraines pass into 
one medial moraine. This will become clear by again referring 
* “ Glaciers of the Alps,” p. 287. 
