[ <;-'!i ] 



Tj X X I X . Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 



[Contiuued from p. 548.] 



April 29th, 1903.— J. J. H. Tcall, Esq., M.A., F.li.S., 

 Vice-President, in the Chair. 

 ''piIE following communications were read: — 

 ^ 1. ' The Atre of tho principal Lake-Basins between the Jura and 

 the Alps.' By Charles S. Du lliche Breller, M.A., Ph.D., A.M.I.C.E., 

 M.I.E.E., F.K.S.E., F.G.S. 



1. In a paper read before the Society last session, the author 

 showed, on the evidence of extensive high-level deposits of Decken- 

 schotter in Subalpine France and Switzerland, that the principal 

 Swiss lake-basins could not have existed at the time when those 

 deposits were formed, during and after the first or Pliocene glaciation 

 of the Alps. In the present paper he deals with the question reserved 

 in the preceding one, that is, to which subsequent period the forma- 

 tion of those lake-basins should be assigned. By the light of further 

 recent investigations in the different localities, he first considers 

 the conditions of the Zurich lake-valley, where the successive 

 glacial and fiuviatile deposits are clearly defined, and then applies 

 his conclusions to the other principal lake-basins lying in the same 

 zone along the edge of the Alps. 



2. The hitherto generally accepted view that the lake-basins are 

 pre-Glacial in the old sense, or were formed during the first inter- 

 Glacial period, rests, in the main, on two arguments : (1) that the 

 alluvia at the lower ends of the lakes are all Glacial, not only from 

 their appearance, but because the materials composing them could 

 only have been transported thence by glaciers, which either passed 

 over the lakes by bridging them, or through them by completely 

 filling them with ice ; and (2) that the zonal bending of the Molasse 

 along the edge of the Alps, to which the lake-basins owe their 

 existence, occurred before the second or maximum glaciation, 

 because at a point in the Lorze ravine (near the Lake of Zug) the 

 Deckenschotter conglomerate dips reversely, that is, up the valley, 

 while the overlying, younger, loose gravel dips in tho opposit,o 

 direction. 



3. The author adduces evidence to show that the deep-level 

 gravel-beds in the Limmat Valley near and below Zurich are essen- 

 tially fiuviatile, composed of the characteristic Alpine material 

 of the Khine and Linth drainage-areas, and in all other respects 

 similar to the gravel carried by the liiver Sihl at the present day. 

 These gravel-beds rest upon Glacial clay of the second glaciation, 

 which fills the Molasse-bed of the valley to a great depth, and are 

 overlain by the moraine-bars and secondary products of the third 

 glaciation, the latter being overlain by, and mixed with, tho 

 post-Glacial alluvia of the Sihl. 



4. He further argues that it is, on mechanical grounds, difficult 

 to conceive how glaciers could either bridge, or completely fill with 



Phil Mag. S. 6. Vol. 6. No. 35. Nov. 1903. 2 T 



