Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/203

Rh AND CIRQUES IN NORWAY AND GREENLAND. 165

bursting, not a scooping out, of the rocks has taken place. The high mountains of Xorway often consist only of loose blocks and stones split by the freezing water. There is some difference between the exposed surface of the mountains and that beneath the glaciers ; for on the latter water at 0° C. is constantly dropping down, easily frozen by every draught of colder air under the glacier, and the glacier itself is always present to remove the blocks.

In the cirques, however, there are often little lakes, and it is more difficult to account for the manner in which the glaciers have ex- cavated these. They are not formed by moraines damming the water, but are true rock-basins ; it does not seem likely that they were mainly scooped out like the great lakes, along the sides of which we see groovings and roches moutonnees one beside the other ; for in the little lakes one often sees sharp-edged blocks covering the bottom. "When the glaciers of the cirques filled these small lakes, so as to leave but little water, it seems probable that the water thus left would freeze in winter, so that the whole tarn would be frozen to the bottom, and the rocks in that way be broken loose. Whatever may be the manner in which these blocks are broken out, we see from their situation and form that a bursting has taken place in these tarns, which are the last works of the glaciers in the cirques.

The cirques which occur isolated in the mountains are not essen- tially different from the valleys which end in a cirque, as often they differ only in size. Thus five valleys ending in cirques and three cirques debouch into the main valley of Yeitestrand, in Sogn; all these are at a much higher level than the main valley and along the same side of it. They both occur in the same way, except that the valleys are longer, their area being as much as twenty -five times as great as that of the cirques. In many cirques at the heads of valleys, both in Xorway and in Greenland, there are lakes with a moraine in front, as in the mountain cirques. These moraines seem to indi- cate that the glaciers remained longest here ; and the excavation of a cirque with a lake in it at the head of the valley was perhaps ac- complished at a later time by an isolated glacier, the upper end of the valley being very well adapted for sheltering a glacier.

Perhaps it may be said that the mountain cirques were most fre- quently formed in the modern period, while the valleys terminated by cirques are older, dating from the close of the Glacial epoch, though some even of these are modern and still in process of forma- tion. It is very difficult, if not impossible, to draw the line between the work of rivers before and of glaciers during the Glacial epoch ; but the valleys terminated by cirques show that the present form of the valleys is due to glaciers.

The relation between the occurrence of Lakes in Norway and the different extents of Glaciers during the Glacial epoch. — In many fjord- valleys of Western Xorway, and in still more flat valleys of Southern Xorway, there is an intimate connexion between the extent of gla- ciers and the occurrence of lakes. A traveller in the districts of Hardanger, Sogn, and Xordfjord, in going from the heads of the

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