f suddenly towards it. We had now a close view of
some of the obstacles which bar the approach to Mont Blanc; the
glacier of Boissons, on which we were about to enter, seemed to me
absolutely impassable. The only relief to the white snow and ice
before us, was an occasional rock, thrusting its sharp point above
their surface, and too steep to permit the snow to lodge on it. One of
these rocks, or rather a chain of them, called the 'Grand Mulet,'
which we had destined for our resting place for the night, was before
us, but far above our heads at the distance of four or five miles; the
glacier, however, still intervened, and appeared to defy all attempts
to approach it.

The glacier of Boissons, like all the glaciers of the Alps, is an
immense mass of ice filling a valley which stretches down the mountain
side, and is formed by the accumulated snow and ice, which are
constantly in the summer months, falling from above. While the
glaciers are thus continually increasing on the surface, the internal
heat of the earth is slowly melting them below. Hence, when they are
large, there generally proceeds from under them a considerable stream:
such are the sources of the Rhine and of the Rhone. Their surface,
often resembles that of a violent agitated sea, suddenly congealed.
They are frequently of several leagues in breadth, and from 100 to 600
feet in depth. The snow which falls on them, to the depth of several
feet every winter, is softened by the sun's rays in summer--and
freezing again at the return of cold weather, but in a more solid
state, forms a successive layer every year. This stratum may be easily
measured, (as each of them is distinctly separated from its neighbour
by a dark line,) at the section made by those cracks, which traverse
every glacier in all directions. These cracks or crevices, are
generally thought to be caused by the irregular sinking of part of the
mass, whose support below has been gradually melted away. They are
formed suddenly, and frequently with a noise that may be heard at the
distance of several miles, and with a shock that makes the
neighbouring country tremble: this effect takes place principally
in summer. These rents are from a few inches to 20, 30, or even
50 or 60 feet in breadth, and generally of immense depth: probably
extending to the bottom of the glacier. They present the greatest
danger and difficulty to the passenger. They are often concealed by a
layer of snow, which gives no ind