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: : 216. The first line here moves five inches a day more than the second; and the second nearly three inches a day more than the third. The reasoning is therefore confirmed. The ice-plug, which is in round numbers one thousand yards long, is shortened by the pressure exerted on its front at the rate of about eight inches a day. 217. A river descending the Valley du Géant would behave in substantially the same fashion. It would have its motion on approaching Trélaporte diminished, and it would pour through the defile with a velocity greater than that of the water behind. § 31. Sliding and Flowing. Hard Ice and Soft Ice. 218. We have thus far confined ourselves to the measurement and discussion of glacier motion; but in our excursions we have noticed many things besides. Here and there, where the ice has retreated from the mountain side, we have seen the rocks fluted, scored, and polished; thus proving that the ice had slidden over them and ground them down. At the source of the Arveiron we noticed the water rushing from beneath the glacier charged with fine matter. All glacier rivers are similarly charged. The Rhone carries its load of matter into the Lake of Geneva; the rush of the river is here arrested, the matter subsides, and the Rhone quits the lake clear and blue. The Lake of Geneva, and many other Swiss lakes, are in part filled up with this matter, and will, in all probability, finally be obliterated by it. 219. One portion of the motion of a glacier is due to this bodily sliding of the mass over its bed. 220. We have seen in our journeys over the glacier streams formed by the melting of the ice, and escaping through cracks and crevasses to the bed of the glacier. The fine matter ground down is thus washed away; the bed is kept lubricated, and the sliding of the ice rendered more easy than it would otherwise be. 221. As a skater also you know how much ice is weakened by a thaw. Before it actually melts it becomes rotten and unsafe. Test such ice with your penknife: you can dig the blade readily into it, or cut the ice with ease. Try good sound ice in the same way: you find it much more resistant. The one, indeed, resembles soft chalk; the other hard stone. 222. Now the Mer de Glace in summer is in this thawing condition. Its ice is rendered soft and yielding by the sun; its motion is thereby facilitated. We have seen that not only does the glacier slide over its bed, but that the upper layers slide over the under ones, and that the centre slides past the sides. The softer and more yielding the ice is, the more free will be this motion, and the more readily also will it be forced through a defile like Trélaporte. 223. But in winter the thaw ceases; the quantity of water reaching the bed of the glacier is diminished or entirely cut off. The ice also, to a certain depth at least, is frozen hard. These considerations would justifythe opinion that in winter the glacier, if it moves at all, must move more slowly than in summer. At all events, the summer measurements give no clue to the winter motion. 224. This point merits examination. I will not, however, ask you to visit the Alps in mid-winter; but, if you allow me, I will be your deputy to the mountains, and report to you faithfully the aspect of the region. and the behaviour of the ice. § 32. Winter on the Mer de Glace. 225. The winter chosen is an inclement one. There is snow in London, snow in Paris, snow in Geneva; snow near Chamouni so deep that the road fences are entirely effaced. On Christmas night-nearly at midnight-1859, your deputy reaches Chamouni. 226. The snow fell heavily on December 26; but on the 27th, during a lull in the storm, we turn out. There are with me four good guides and a porter. They tie planks to their feet to prevent them from sinking in the snow; I neglect this precaution and sink often to the waist. Four or five times during our ascent the slope cracks with an explosive sound, and the snow threatens to come down in avalanches.* The freshly-fallen snow was in that particular condition which causes its granules to adhere, and hence every flake falling on the trees had been retained there. The laden pines presented beautiful and often fantastic forms. 227. After five hours and a half of arduous work the Montanvert was attained. We unlocked the forsaken auberge, round which the snow was reared in buttresses. I have already spoken of the complex play of crystallising * Four years later, viz. in the spring of 1863, a mighty climber and noble guide and companion of mine, named Johann Joseph Bennen, was lost, through the cracking and subsequent slipping of snow on such a slope. forces. The frost-figures on the window-panes of the auberge were wonderful: mimic shrubs and ferns wrought by the building power while hampered by the adhesion between the glass and the film in which it worked. The appearance of the glacier was very impres sive; all sounds were stilled. The cascades which in summer fill the air with their music were silent, hanging from the ledges of the rocks in fluted columns of ice. The surface of the glacier was obviously higher than it had been in summer; suggesting the thought that while the winter cold maintained the lower end of the glacier |