316 DE. C. S. DTTEICHE PEELLEE ON THE [Allg. I904, 



20. Phenomena bearing upon the Age of the Lake of Geneva. 

 By C. S. Du Riche Peellee, M.A., Ph.i)., A.M.I.C.E., M.I.E.E., 

 F.R.8.E., F.G.S. (Read May 11th, 1904.) 



[Abstract.] 



Following up his investigations concerning the age of the 

 principal Alpine lake-basins, the Author has, during a recent 

 prolonged stay on the Lake of Geneva, examined the low-level 

 gravel-beds and other alluvia in the Rhone Valley, from Geneva 

 to the Jura-bar near Fort de l'Ecluse, as well as the high-level 

 gravel-beds of La Cote above Rolle and of the Jorat district above 

 Lausanne, and, further, the rock-formations on both sides of the 

 lake, in view of evidence of flexures as the primary cause of 

 the formation of the present deep lake-basin. 



After describing the phenomena around the Lake of Geneva, and 

 comparing them with those around the Lake of Zurich, he is led to 

 the following conclusions : — 



(1) The low-level gravel-beds of the Rhone Yalley near Geneva. 



overlying the Molasse and underlying the glacial alluvia, 

 are, like the deep-level gravel-beds of the Limmat Yalle)- 

 near Zurich, fluviatile deposits of the second Interglacial 

 Period, and were formed before the present deep lake-basin 

 came into existence. 



(2) The high-level gravel-beds of La Cote above Rolle and of the 



Jorat district above Lausanne are, like the corresponding 

 deposits of the Uetliberg near Zurich, and of the Dombes and 

 of Lyons, true Deckenschotter. Hence the term alluvion 

 ancienne should, in its proper acceptation, only apply to 

 the high-level deposits. 



(3) The formation of the present deep lake-basin of Geneva was, 



like that of Zurich, primarily due to the lowering of the 

 valley-floor by flexures of the Molasse and its contact- 

 zones, posterior to the maximum glaciation, as evidenced 

 more especially hy the reverse dip of the old erosion- 

 terraces between Lausanne, Vevey, and Clarens. 



The Author holds that the concord of evidence in the two cases 

 strengthens the conclusion, already arrived at by analogy in his 

 previous paper, 1 that the Lake of Geneva, together with the other 

 principal zonal lakes between the Alps and the Jura, was formed 

 under similar conditions and at the same time as the Lake of 

 Zurich, that is, towards the close of the Glacial Period : indeed, the 



1 Quart. Journ. Geol. Soc. vol. lx (1904) p. 65. 



