196 PROCEEDINGS OF THE GEOLOaiCAL SOCIETY. [Mar. 5, 



th.e ice, gradually declining in thickness, exercised less grinding 

 power. In this manner I believe the troughs were formed in which 

 lie the three lakes near Neuchatel ; and when the ice finally retreated, 

 the ordinary drainage of the country filled them with water, the 

 cliffs on the south-eastern side of the Lake of Neuchatel and other 

 changes of the form of the ground having since been produced or 

 modified by watery erosion and the local deposition of silt and allu- 

 vial gravel. 



The Lake of Thun.— The Lake of Thun is 1825 feet above the 

 sea, and 776 feet deep. Its bottom is therefore 1049 feet above the 

 sea. It is about 10 miles in length, 1 j broad, and its length chiefly 

 cuts across the strike of rocks of Secondary and Miocene age. The 

 Lake of Brienz (about the same size) is more remarkable ; for, while 

 its level is 1850 feet above the sea, its depth is more than 2000 feet : 

 so that its bottom is at least between 100 and 200 feet below the 

 level of the sea. Before the formation of the alluvial plain between, 

 these two lakes were probably united ; and whether or not this was 

 the case, it is evident, from its great depth, that the Lake of Brienz 

 lies in a true rock-basin. Even if below Thun the rocks do not crop 

 nearer than Solothurn, the Lake of Thun still hes in a rocky hoUow 

 more than 600 feet deep, both hollows having, I believe, been deep- 

 ened by the great old glacier of the Aar (No. 2 in the Map), the ice of 

 which was so thick, that above Brienz it overflowed into the valley of 

 Sarnen by the Brunig, about 1460 feet above the Aar below Meyrin- 

 gen, and sent off a branch which scooped out the hollows of the Lakes 

 of Lungern and of Sarnen on its course towards Alpnach on the Lake 

 of Lucerne. 



The Lake of Zug. — The Lake of Zug is about 9 miles long, from 

 1 to 2|- wide, 1361 feet above the sea, and 1279 feet deep ; and 

 its bottom is therefore only 82 feet above the sea. The whole is 

 surrounded by Miocene strata, the strike of which the lake cuts across, 

 and its great depth clearly shows that it lies in a rock-basin. 



The Lalce of Lucerne. — The Lake of the Eour Cantons (Lucerne) 

 ramifies among the mountains and extends its arms in various direc- 

 tions. In its lower part, the branches that run N.E. to Kussnach 

 and S.W. towards Gestad lie partly in the strike of the Miocene 

 and older strata ; but for the most part it runs across the average 

 strike of the Eocene and Secondary rocks, between banks, some- 

 times precipitous, that rise in noble cliffs sometimes more than 2000 

 feet above the water. Its height is 1428 feet above the sea, and 

 its recorded depth 853 feet ; but the shape of the banks and the 

 round number of 800 Erench feet make it likely that it may con- 

 tain deeper gulfs than have yet been plumbed. If not, then its 

 bottom is 575 feet above the sea ; and those acquainted with the 

 shape of the ground by Lucerne will easily be convinced that the lake 

 lies in 'an actual rock-basin. The steepness of the walls of this lake 

 more resembles the sides of a rent than those of any of the basins yet 

 described, and the re-entering angles of rock opposite curving bays 

 have been cited as evidences of fracture, one side being supposed to 

 fit into the other. But in most cli% valleys of aqueous erosion there 



