i88o.] 
On Water and Air . 
3i9 
If I were to take a quantity of snow and subject it to 
pressure I should compress this snow into solid ice. Now 
the mountains surrounding this region are continually dis- 
charging their snows upon these great plateaux, and this 
continuous accumulation compresses the snow into solid ice ; 
and rigid as this ice seems it is always moving downwards. 
It moves down almost like water, and fills the valley of the 
Col du Geant, forming the glacier of that name. This 
glacier is joined by another called the Glacier de Lechaud ; 
and here another glacier comes down, falling apparently in 
broken fragments, in a kind of cascade, which is called the 
Cascade du Talefre; and these three glaciers unite and 
form the celebrated Mer de Glace. You observe here the 
extraordinary fadt that these great and wide glaciers squeeze 
themselves down through this narrow valley of the Mer de 
Glace at Trelaporte, as if the ice in point of fadt were 
water. The quantity of squeezing endured at this place 
called Trelaporte is very great. The glacier coming down 
from the Col du Geant is 1134 yards across ; the one from 
the Jorasse, the Glacier de Lechaud, is 825 yards across. 
The glacier coming down from the Talefre is, at a certain 
place near the cascade, 638 yards across, and the sum of 
these three glaciers amounts to 2597 yards in width. All 
these three are squeezed together through that defile at 
Trelaporte, which is only 893 yards wide. This gives you 
an idea of the tremendous power with which these ice- 
masses are forced forward in order to form these glaciers. 
I say forced forward, and that implies, of course, that the 
glaciers are always in motion ; and this is the case winter 
and summer. The summer motion of this Mer de Glace 
amounts to a certain number of inches per day; the winter 
motion is about half the amount. The summer motion is 
on the average about 30 inches a day ; the winter motion is 
about 15 inches a day, the ice being more rigid and less 
yielding in winter than in summer. 
You see the motion of the ice through this valley ; it 
twists round and turns, and imitates, in all its movements, 
the motion of a river. Many distinguished men have worked 
at these glaciers, but perhaps none have contributed more 
to our knowledge of the matter than two men who are now 
no more — the celebrated Agassiz, who died some time ago 
in America, and the celebrated Principal Forbes of St. 
Andrews. 
Here is a rough diagram of the Mer de Glace with certain 
lines drawn across it (Fig. 31). The velocity of the glacier 
where those lines are drawn has been determined. I will 
VOL II. (THIRD SERIES). 2 A 
