582 DK. C. S. DtT EICHE PEELLEE ON GLACIAL [Aug. 1 896,,. 



the Lorze ravine north of the stalactite-caves, the dip up the valley 

 being in these two cases about 1°. It is important to note that 

 not only at the two points just mentioned, but also at Altschloss, 

 the contact of the Molasse underlying the Deckenschotter is near 

 contour 550 ; that the reverse dip (i. e. 1°) of the terraces of 

 erosion bordering the Lake of Zurich is approximately the same 

 as that in the Sihl and Lorze ravines ; and, lastly, that the two* 

 points noticed in those ravines lie, together with Altschloss, in a 

 line parallel to the strike of the Alps. In other words, this line- 

 marks the syncline of the subsidence-zone, and it is to this sub- 

 sidence that the Lake of Zurich primarily owes its origin. 



As regards the Deckenschotter deposits, the evidence of reverse 

 dips on and near the Albishorn — indeed, as I have already shown, of 

 the high-level occurrences generally — is either doubtful, inconclusive^ 

 or directly negative ; and the same applies to the lower-level deposits- 

 of Au and Altschloss, as well as to those in the Lorze and Sihl 

 ravines. The apparent or occasional slight dip of these deposits,, 

 either in one direction or the other, is, in my view, due simply to- 

 their character of detritus-cones, with the exception of one case on 

 the Hirzel road near the village of Oberkellenholz, where, at con- 

 tour 647, a cliff of Deckenschotter, crossing that road at right 

 angles, drops, according to my measurements, at an angle of 2| a 

 for some distance towards the Sihl ravine. Having regard to the 

 general reverse dip of the Molasse in this region, varying from 

 1° to 5° and 25°, the inclination of the Deckenschotter cliff just 

 noticed warrants the inference that the zonal subsidence between 

 the Lake of Ziirich and that of Zug, and with it the formation of 

 the Zurich lake-basin, took place after the deposition of that con- 

 glomerate, probably between the first and second glaciations, and at 

 any rate in Pleistocene times. 



The approximate depth of this subsidence may be determined 

 from the difference of level between the anticline near the Albishorn 

 and the syncline already referred to. Although the Molasse strata 

 of the Albis range have, in places, a dip of as much as 1|° down 

 the valley, the crest-line of the rock, irregularly overlain by glacial 

 deposits, is practically horizontal, since at both ends, that is, at the 

 Uetliberg and near the Albishorn, and also midway, the solid rock 

 appears near contour 850. The difference of level between the 

 Molasse at the Albishorn and that at the three synclinal points is 

 300 metres, and this is therefore the approximate maximum depth 

 of subsidence of the zone between the lakes of Zurich and Zug, and 

 hence also of the old Zurich valley. 1 



If the irregularly-shaped glacial deposits, under which the 

 Molasse of the Hirzel and Menzingen plateau is now buried, could 



1 By an elaborate calculation, Dr. Aeppli (Beitrage, vol. xxxiv. pp. 75, 76) 

 arrives at a subsidence of 425 metres, his computation being based, not upon the 

 contact-points of the solid rock (obviously the only reliable standard), but upon 

 the summit-levels of the Deckenschotter deposits, which latter may, however, 

 have undergone many changes since they were formed. Wettstein (' Geol. 

 JZiirich,' p. 57) and Dr. Du Pasquier (Beitrage, vol. xxxi. p. 116) arrived at about 



