Vol. 52.] GLACIAL DEPOSITS UK STTBALPINE SWITZERLAND. 559 



Although these characteristics conspicuously distinguish the 

 Deckenschotter from the older Miocene Nagelfluh, and — as regards 

 the cliff-like appearance as well as the advanced calcification — also 

 from the younger, Pleistocene gravels, the conglomerate varies 

 greatly according to its position, to its derivation, and to the time 

 of its deposition within the limits of the first Glacial period. And 

 this is the more natural when we reflect how many must have been 

 the glacial oscillations within that time, and that every advance of 

 the glacier marks a stoppage, and every recession of the same marks 

 a renewal of erosion at the terminal moraine. If, broadly speaking, 

 we assume, in accordance with the general periodicity of Alpine 

 glaciers of our own day, an alternate advance and recession of the 

 glaciers of the first Ice-period every fifty years, there must have 

 occurred in the space of, say, 5000 years, at least 100 semi- 

 secular oscillations, during half of which glacio-fluviatile material 

 must have been deposited in varying form, at various points, and at 

 widely-varying levels. 



Origin. — As I have already pointed out in previous papers, there 

 is no room for doubt that the Deckenschotter of the Zurich district 

 was, in the main, deposited by streams issuing from an extensive 

 Linth glacier which, descending from the Glarner Alps, advanced to 

 within a few miles of the lower Aare valley, and, together with 

 the Rhine glacier on its right and the Sihl and Reuss glaciers on its 

 left, formed, towards the end of the Pliocene period, one great 

 Subalpine ice-sheet. 



Although the moraine of these glaciers yielded part of the 

 material of which the Deckenschotter was built up, the bulk of the 

 conglomerate was not, in my opinion, transported by the glaciers 

 from any great distance, but is derived from the enormous accu- 

 mulations of Miocene Nagelfluh at the foot of the Alps. In 

 this view I was confirmed by an examination of a large number 

 of pits and natural sections of comparatively loose, both calcareous 

 and polygene, Miocene Nagelfluh in the hills flanking the lake of 

 Zurich. J This youngest Nagelfluh-zone, which corresponds to the 

 Upper (freshwater) Molasse, extends longitudinally from the Lake of 

 ■Constance to that of Thun and transversely as far as the Uetliberg 

 near Zurich, and all the rocks occurring in the same are also largely 

 represented in the Deckenschotter as well as in the younger, Pleisto- 

 cene gravels ; while the large boulders of Miocene Nagelfluh, which 

 are occasionally found embedded in the Deckenschotter, are derived 

 from the coarser and extremely hard conglomerate of the older, i. e. 

 the Rigi, Rossberg, and Speer Nagelfluh-zones corresponding to the 

 Lower (freshwater) Molasse. 2 Thus the successive deposition of 

 Deckenschotter and Pleistocene gravels in three series, each of 



1 The pits and sections are those near Binz, Pfaffhausen, and Weilerhof in 

 the hills on the right, and near Riiti and Wadenswil on the left of the Lake 

 of Zurich. 



3 Strictly speaking, the Molasse and Miocene Nagelfluh formation comprises, 

 besides the Lower freshwater, Marine, and Upper freshwater series, also the 

 isolated Marine beds of the so-called Red (Oligocene) Molasse. 



