Vol. 51.] AND INTERGLACIAL DEPOSITS IN SWITZERLAND. 377 



pelled to scoop out its present bed, which lies closely parallel to, but 

 outside, the drainage-area of the Lake of Zurich, as shown in the 

 map, fig. 2, p. 370. 



In his memoir already quoted, Dr. Du Pasquier refers incidentally 

 to the Lorze Valley Nagelfluh and regards it as contemporaneous 

 with the Uznach and Diirnten lignite-deposits, that is, as belonging 

 to the second interglacial period. But two facts militate against this 

 conclusion : first, that the Pliocene ' Cavernous Nagelfluh ' of the 

 Uetliberg near Zurich is indisputably derived from the Linth basin 

 or Glarner Alps, as evidenced by the predominance of red Sernifite- 

 pebbles, so that at that time the Sihl must have been already 

 deflected to the Eeuss basin, where it formed the deposit under notice; 

 and secondly, that the Sihl Nagelfluh of the Lorze Valley exhibits 

 all the characteristics of the Uetliberg Nagelfluh save, of course, in 

 the composition of the pebbles. These in the Sihl deposit are 

 derived chiefly from the Neocomian and Flysch limestone and sand- 

 stone strata of the upper course of that river. The Lorze Valley- 

 deposit must therefore be regarded as the indirect product of the 

 first and not the second glaciation, and the same applies to the 

 smaller outlying deposits of Blickendorf and Sihlbrugg, near Baar 

 (9 and 10, fig. 2, p. 370), which probably mark an old serpentine 

 course of the river Sihl, and are at any rate part of the same 

 original complex. 1 



As regards the underlying moraine, Prof. Heim refers it, as well 

 as the overlying moraine, to the Eeuss glaciers. 2 No doubt the 

 ancient course of the Keuss was not through the lower part of the 

 Lake of Lucerne, but from Brunnen through the Goldau Valley and 

 through the present Lake of Zug (figs. 1 and 2, pp. 369, 370) ; but, so 

 far as my examination on the spot goes, the gneiss and granite- 

 boulders characteristic of the Reuss drainage-area are absent in the 

 morainic deposits of the Lorze Valley properly so-called. Hence 

 these deposits must be referred to the old Sihl glacier, and in part 

 to the Aegeri glacier. 



In connexion with the Lorze Valley-deposit, it maybe mentioned 

 that the indiscriminate use of the terms ' delta ' and ' debris-cone,' 

 as applied to this and similar gravel-beds, is a fruitful source of 

 confusion. Prof. Heim and others speak of the Lorze Valley-deposit 

 as an old delta, whilst Dr. Du Pasquier terms it a ' schuttkegel ' 

 or debris-cone. As the last-named writer justly points out, deltas 

 are subaqueous deposits formed by rivers discharging into still or 

 sluggish water such as the main affluents of lakes or of the sea, or 

 into flowing water, such as the tributaries of large rivers ; whereas 

 debris-cones are accumulations formed on terra firma by lateral 

 torrents. The Sihl, being at the time an affluent of the Eeuss, 

 must have formed in the first instance an extensive delta which 



1 [Since this paper was read, Dr. Aeppli, of Zurich, has referred to the Lorze 

 Valley, Blickendorf, and Sihlbrugg deposits in a monograph on ' Die Entstehung 

 des Ziirichsees' (Beitrage zur geol. Karte d. Schweiz, 1895). His conclusions 

 as regards the Lorze Valley-deposit substantially agree with mine, while he 

 refers the smaller outlying deposits to a younger glaciation, a conjecture of 

 which the accuracy may, however, fairly be doubted. — May, 1895.J 



2 Neujahrschrift der Naturf. Gesellsc'haft Zurich, 1891. 



