66 DR. DU RICHE PRELLER OX THE AGE OF THE [Feb. I904, 



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

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

 2 to 8 miles in width and from 470 to 1020 feet in depth, the 

 quantity of water to be displaced and expelled in the individual 

 cases ranging from 3500 million to 90,000 million cubic metres or 

 tons. 



5. As regards the more recently-advanced argument of the 

 younger moraine-banks flanking the Lake of Zurich and of the 

 Deckenschotter in the Lorze Valley near Zug, the Author points 

 out that it is not borne out by the evidence on the ground, and 

 that, apart from the difficulty of differentiating the second and 

 third glaciation-materials in both localities, it is obviously hazardous 

 to deduce from purely-local phenomena of this kind the date of the 

 zonal bending affecting 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 

 glacier had already reached its maximum extension, about 10 miles 

 below Zurich ; that the zonal subsidence continued throughout the 

 retreat of the ice ; and that the simultaneous formation of the lake- 

 basin should, therefore, be assigned to the end of the Glacial Period, 

 after which the original basin was, notably at its upper end, 

 restricted to its present dimensions by post-Glacial alluvia. 



7. In conclusion, the Author shows that the same arguments 

 apply, in the main, also to the origin and age of the other principal 

 zonal lake-basins, which he illustrates by longitudinal sections. In 

 his view, the position and depth of these basins, as well as the 

 intervening ground, point to the probability that the bending took 

 place not only along one line, but along several, more or less 

 parallel, not always continuous lines within the zone between the 

 Alps and the Jura; that the bending was by no means of uniform 

 depth ; and that, therefore, the Alps did not subside as a rigid mass, 

 but that the zonal bending along their edge merely extended 

 locally for some distance from the deepest points of the lake-basins 

 along the floors of the principal Alpine river- valleys. 



Discussiox. 



Prof. Boxney said that he had always felt great difficulty in 

 understanding how the glaciers made their way through the lake- 

 basins, supposing these to have been in existence at the time of the 

 great glaciation. But what had most impressed him was the fact 

 that the Zurich gravels were true river-gravels, and quite different 

 from deposits formed in proximity to a glacier. Of this difference 

 he gave details, pointing out that a stone must travel not a few 

 miles (much longer than the distance determined experimentally 

 by Daubree) in order to become well rounded. So that neither the 



