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The lakes and water-basins may be classified in four groups, each lakes with its own peculiar scenery and distinct mode of origin. 1. Glen lakes, 2. Rock-tarns, 3. Moraine-tarns, 4. Lakes of the plains.
Glen Lakes are those which occupy portions of glens. They are depressions in the valleys, not due to local heaping up of detritus, but true rock-basins, often of great depth. Much discussion has arisen as to their mode of origin, but it is probable they were caused by the erosive action of ice, since glaciers occupied the glens where they occur and wore down the rocks along the sides and bottom: but it is a point of difficulty in this theory whether ice could have eroded the deepest of the hollows. In any circumstances the lakes must be of recent geological date. Any such basins belonging to the time of the folding ot the crystaline schists would have been filled up and effaced long ago. Indeed so rapid is the infilling by the torrents which sweep down detritus from the surrounding heights that even the existing lakes are visibly diminishing Glen lakes are almost wholly confined to the western half of the Highlands, where they form the largest sheets of fresh water. Hardly any lakes are to be seen east of a line drawn from Inverness to Perth. West of that line, however, they abound in both the longitudinal and the transverse valleys. The most remarkable line of them is that which fills up much of the Great Glen, Loch Ness being the largest. Other important longitudinal lakes are Lochs Tay, Awe, Ericht and Shiel. The most picturesque glen lakes however lie in transverse valleys, which being cut across the strike of the rocks present greater variety and, usually, abruptness,of outline. Lochs Lomond, Katrine and Lubnaig in the southern Hightands, and Lochs Maree and Ivtore in the north, are conspicuous examples. |
