280 Reports and Proceedings — Qeological Society of London, 



recent investigations in the different localities, he first considers 

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

 glacial and fluviatile deposits are clearly defined, and then applies 

 his conclusions to the other princijDal 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 the opposite 

 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 fluviatile, composed of the characteristic Alpine material 

 of the Ehine and Linth drainage areas, and in all other respects 

 similar to the gravel carried by the Eiver 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 the 

 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 

 ice, such extensive basins as those of the principal Alpine lakes, from 

 2 to 8 miles in width and from 470 to 1,020 feet in depth, the 

 quantity of water to be displaced and expelled in the individual 

 cases ranging from 3,500 million to 90,000 million cubic metres 

 or tons. 



(5) As regards the more recently enunciated argument of the 

 Deckenschotter and overlying gravel exposure in the Lorze 

 Valley, the author points out that, apart from the difficulty of 

 differentiating the second and third glaciation materials in that 

 locality, it is obviously hazardous to deduce from a purely local 

 phenomenon of this kind, and more especially from any dip of loose 

 gravel — in contrast with rock or compact conglomerate — the date of 

 the zonal bending afiecting six valley systems, and extending over 

 more than 200 miles along the edge of the Alps. 



(6) The author's investigations point to the conclusion that the 

 deep-level Limmat gravel-beds, overlain by the moraine-bars of 

 the third glaciation, were deposited by a river during the second 

 inter-Glacial period ; that the lowering of the valley floor was 

 initiated in the course of the third glaciation, probably when the 



