GLACIAL EROSIOX OF LAKE BASINS 115 



which are supposed to have been moved to cause lakes are 

 free to take any upward or downward curves, and as the 

 source of motion is certainly deep-seated those curves will 

 usually be of very gradual curvature. Yet in the small 

 lake of Annecy there are two separate basins ; in Lake 

 Bourget also two ; in the small lake of Aiguebellette, in 

 Savoy, there are three distinct basins of very different 

 depths ; and in the Lac de St. Point, about four miles long, 

 there are also three separate tiat basins. In Switzerland 

 the same phenomenon is often found. In the Lake of 

 Neufchatel there are three basins separated by ridges from 

 twenty to thirty feet above the deeper parts. The small 

 Lac de Joux, at the head of a high valley in the Jura, has 

 also three shallow basins. Lake Zurich consists of three 

 well-marked basins. The exceedingly irregular Lake of 

 Lucerne, formed by the confluence of many valleys meeting 

 at various angles hemmed in by precipitous mountains, 

 has eight distinct basins, mostly separated by shallows at 

 the narrow openings between opposing mountain ridges. 

 This is exactly what would result from glacier action, the 

 grinding power of which must always be at a maximum 

 in the wider parts of valleys, where the weight of the ice 

 could exert its full force and the motion be least impeded. 

 On the subsidence or curvature theory, however, there is 

 no reason why the greatest depth should occur in one part 

 rather than in another, while separate basins in the 

 variously diverging arms of one lake seem most im- 

 probable. The lakes of Thun and Brienz form two basins 

 of what was evidently once a single lake. The upper or 

 Brienz basin is enormously deep, over two thousand feet, 

 and the reason is obvious. The combined glaciers of the 

 Lauterbrunnen and Grindelwald valleys entered the main 

 valley in a direction almost opposite to that of the Aare, 

 piling up the ice against the great barrier of the Rieder 

 Grat, so that it at length flowed downward with greatly 

 increased grinding power; while lower down, towards 

 Thun, the valley opens widely and would thus allow the 

 ice to spread out with greatly diminished thickness. In 

 our own country Loch Lomond and Ullswater have been 

 found to consist of several distinct basins, and in none 



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