Page:The journal of the Royal Geographic Society of London. Volume 34, 1864. (IA s572id13663720).pdf/311

Rh they are not so steep towards their summits, where there is generally a large area presenting slopes on which snow could rest under circumstances favourable for its accumulation, and form the source of glaciers which would descend into the lower valleys. Pembroke Peak (6623 feet) is covered with perpetual snow, which on its south-east face extends as low as 4000 feet, with a slope of 20° to 30°, and there terminates in a cliff of true glacial ice, judging by its intense blue tint compared with that of the surrounding snow; and did it not overhang a precipice, this ice would doubtless descend as a glacier to a very low altitude. Now the average height of the mountain-ridges is nearly 6000 feet, and with the present conditions of climate, an elevation of the land equal to 2000 feet would, according to the best estimate I can form, raise about six-tenths of the area of this mountain district to that altitude, which is certainly considerably above the snow-line in the strict sense; that is the line above which the snow never disappears during the summer, unless by gravitation after assuming the glacier form by regelation.

It is a mistake to estimate the size of glaciers generated from a mountain-range merely by its altitude, as it is truly the area which in the district is elevated above the snow-line that determines their extent. If this be the case, the area must always be diminishing rapidly from the eroding action of the descending ice, and therefore the extent of the glaciers must also dimmish. Judging from the structure of the sounds on the west side of the mountains, and that of the lake district on the east side, I am inclined to think that the opposite sides of this mountain-range have undergone repeated and alternate oscillations to the extent of at least 1000 feet in either direction from a nominal point; and that the western district being at present near to the period of greatest depression, the re-elevation of the land to the other extreme would be almost sufficient to extend the glaciers to their ancient limits, for the residual excess of cold to effect this could easily be accounted for by the necessary alterations in the physical geography of the country which would accompany such re-elevation. The immense lapse of time and the number of secular returns of these conditions is well shown by the remains of the high-level valleys, which were the wide channels for glaciers of earlier date, but are now represented as fringing shelves along the sides of more profound valleys, just like the terraces skirting the valley of a river which is changing its course from side to side of a gradually deepening channel.

From the altitude we had attained I could see that there was no hope of finding a saddle at the head of this valley, whereby communication could be had with the inhabited districts on the east side. All further progress appeared to be barred by precipitous