Page:Popular Science Monthly Volume 45.djvu/54

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relation to the form and slope of the valleys and the intensity of the glaciation to which they have been subject. In our own country we have in Wales a small number of valley lakes; in the Lake District, where the ice-sheet can be proved to have been much thicker and to have lasted longer, we have more numerous, larger, and deeper lakes; and in Scotland, still more severely glaciated, the lakes are yet more numerous, many of those in the west opening out to the sea and forming the lochs and sounds of the western Highlands. Coming to Switzerland, which, as we have seen, bears indications of glaciation on a most gigantic scale, we find a grand series of valley lakes both on the north and south, situated for the most part in the tracks of those enormous glaciers whose former existence and great development are clearly proved by the vast moraines of northern Italy and the traveled blocks of Switzerland and France. In Scandinavia, where the Ice age reigned longest and with greatest power, lakes abound in almost all the valleys of the eastern slope, while on the west the fiords or submerged lakes are equally characteristic.

In North America, to the south of the St. Lawrence River and of Lakes Ontario and Erie, there are numbers of true valley lakes, as there are also in Canada, besides innumerable others scattered over the open country, especially in the north, where the ice-sheet must have been thickest and have lingered longest. And in the southern hemisphere we have, in New Zealand, a reproduction of these phenomena—a grand mountain range with existing glaciers, indications that these glaciers were recently much more extensive, a series of fine valley lakes forming a true lake district, rivaling that of Switzerland in extent and beauty, with fiords on the southwest coast comparable with those of Norway.

Besides these valley lakes there are two other kinds of lakes always found in strongly glaciated regions. These are Alpine tarns—small lakes occurring at high elevations and very often at the heads of valleys under lofty precipices; and small or large plateau or low-level lakes which occur literally by thousands in northern Canada, in Sweden, Finland, Lapland, and northwestern Russia. The valley lakes and the Alpine tarns are admitted by all geologists to be mostly true rock basins, while the plateau and low-country lakes are many of them hollows in the drift with which much of the country is covered, though rock basins are also not infrequent.

Here, then, we see a remarkable association of lakes of various kinds with highly glaciated regions. The question is whether there is any relation of cause and effect in the association; and to determine this we must take a rapid survey of other mountain regions where indications of ice action are comparatively slight or altogether wanting, and see whether similar lakes