203. Furnished with the knowledge which these labours and measurements have given us, let us once more climb to our station beside the Cleft under the Aiguille de Charmoz. At our first visit we saw the medial moraines of the glacier, but we knew nothing about their cause. We now know that they mark upon the trunk its tributary glaciers. Cast your eye, then, first upon the Glacier du Géant; realise its width in its own valley, and see how much it is narrowed at Trélaporte. The broad ice-stream of the Léchaud is still more surprising, being squeezed upon the Mer de Glace to a narrow white band between its bounding moraines. The Talèfre undergoes similar compression. Let us now descend, shake out our chain, measure, and express in numbers the width of the tributaries, and the actual amount of compression suffered at Trélaporte.
204. We find the width of the Glacier du Géant to be 5,155 links, or 1,134 yards.
205. The width of the Glacier de Léchaud we find to be 3,725 links, or 825 yards.
206. The width of the Talèfre we find to be 2,900 links, or 638 yards.
207. The sum of the widths of the three branch glaciers is therefore 2,597 yards.
208. At Trélaporte these three branches are forced through a gorge 893 yards wide, or one-third of their previous width, at the rate of twenty inches a day.
209. If we limit our view to the Glacier de Léchaud, the facts are still more astonishing. Previous to its junction with the Talèfre, this glacier has a width of 825 yards; in passing through the jaws of the granite vice at Trélaporte, its width is reduced to eighty-eight yards, or in round numbers to one-tenth of its previous width. (Look to the sketch on the next page.)
SKETCH-PLAN SHOWING THE MORAINES, a, b, c, d, e, OF THE MER DE GLACE.