the Alpine Lakes and Valleys. 213 



neighbourhood run nearly north-east, follow for a great dis- 

 tance the curve of the lake, and towards the frontier of the 

 Valais take an easterly direction, as does the lake itself between 

 Rolle and Villeneuve." This form may be recognized in my 

 geological map of Savoy. 



These great features, so characteristic of the region of the 

 Alps which border upon us, establish an evident relation be- 

 tween the form and position of the lake-basin, the orography 

 of the ground, and the cause which has elevated the mass of 

 the Alps above the mean level of the continent. 



The position of most of the Alpine lakes reveals to us, again, 

 the relation which subsists between the mountains and the 

 lake-basins : nearly all lie either on the borders of the Alps, or 

 at the junction of the beds of Mollasse with hard calcareous 

 chains. They frequently even penetrate the interior of the 

 chains — allowing that the marshes, which are almost always at 

 their upper end, form part of the lakes. 



Such are the lakes of Geneva, of Thun, Lucerne, those of 

 Zurich and Wallenstadt (which form only one lake in a geo- 

 graphical point of view), and also the Lake of Constance. In the 

 Bavarian and Austrian Alps, again, are found the lakes of Wal- 

 chen, Kochel, Schlier, Mond, Atter, Traun, &c, all on the borders 

 of the Alps. Is this very remarkable position the result of chance ? 

 or is it not likely that in the law of the structure of the Alps 

 there is a circumstance which has determined the formation of 

 the lake-basins. This had been pointed out by De Saussure when, 

 in describing the mountains lying on the right bank of the valley 

 of the Arve, he remarked that the innermost turned their backs 

 towards the exterior part of the Alps *, but that the outer 

 chains turn their backs to the central chain ; that is to say, 

 that their curves are brought up on a line with the Lake of 

 Geneva. 



Since the time of De Saussure light has been thrown on the 

 question, and the papers which you yourself have published have 

 contributed largely to the elucidation of this subject f. It is 

 now recognized that over the greater part of the enormous 

 distance which separates the environs of Geneva from the 

 eastern Alps of Austria, there is a prolonged reversal of strata, 

 so that very often the older beds repose upon the newer. One 

 can understand that such a great disturbance in the strata 

 should have produced a subsidence in those which are beneath 

 the surface by a sort of reciprocating movement (bascule). As 

 regards the Lake of Geneva in particular, this reversal has 

 been clearly pointed out on the two banks — on the northern at 



* Voyages, § 281. 



t Quart. Joum. Geol. Soc. 1848, vol. v. pp. 182, 195, 197, 200. 



