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 indication on its surface, of its want of solidity; and it often happens that the chamois hunter, notwithstanding all his caution, suddenly sinks through this treacherous veil into the chasm beneath. We remained a couple of hours at our resting place, to take some refreshment, and to regain strength for our next difficult task. Jacques Balmat accompanied us this far, to point out the best means of attaining that spot on which he was the first to set foot; but the infirmities of age prevented him from accompanying us farther. Our feet seemed to linger, and to leave with reluctance the last ground they were to touch until the period of our return.