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.) [Illustration: SKETCH-PLAN SHOWING THE MORAINES, _a_, _b_, _c_, _d_, _e_, OF THE MER DE GLACE.] 210. Are we to understand by this that the ice of the Léchaud is squeezed to one-tenth of its former _volume_? By no means. It is mainly a change of _form_, not of volume, that occurs at Trélaporte. Previous to its compression, the glacier resembles a plate of ice _lying flat_ upon its bed. After its compression, it resembles a plate _fixed upon its edge_. The squeezing, doubtless, has deepened the ice. § 30. _Longitudinal Compression of a Glacier._ 211. The ice is forced through the gorge at Trélaporte by a pressure from behind; in fact the Glacier du Géant, immediately above Trélaporte, represents a piston or a plug which drives the ice through the gorge. What effect must this pressure have upon the plug itself? Reasoning alone renders it probable that the pressure will shorten the plug; that the lower part of the Glacier du Géant will to some extent yield to the pressure from behind. 212. Let us test this notion. About three-quarters of a mile above the Tacul, and on the mountain slope to the left as we ascend, we observe a patch of verdure. Thither we climb; there we plant our theodolite, and set out across the Glacier du Géant, a line, which we will call line No. 1 (F F' upon sketch, p. 68). 213. About a quarter of a mile lower down we find a practicable couloir on the mountain side; we ascend it, reach a suitable platform, plant our instrument, and set out a second line, No. 2 (G G' upon sketch). We must hasten our work here, for along this couloir stones are discharged from a small glacier which rests upon the slope of Mont Tacul. 214. Still lower down by another quarter of a mile, which brings us near the Tacul, we set out a third line, No. 3 (H H' upon sketch), across the glacier. 215. The daily motion of the centres of these three lines is as follows:-- Inches Distances asunder No. 1 50·55 } } 545 yards. No. 2 15·43 } } 487 " No. 3 12·75 }