32 Dr. Du Riche Preller — Three Glaciations of Switzerland. 



Third Glaciation. — The enormous second glaciation, during which 

 the North of Switzerland must have presented an appearance similar 

 to that of Greenland at the present time, was followed, after another 

 interglacial (Middle Pleistocene) period, by the third glaciation, the 

 last of diluvial times. Among the deposits of this last glaciation 

 are those on the low range of hills on the left bank of the lake above 

 Zurich, and here I examined more especially the extensive quarries 

 on the summit of the ridge and near the Froschen-lake, close to the 

 high road which connects Thalweil (on the lake) with Gattikon (in 

 the Sihl Valley). In these quarries (540 metres or 1780 feet above 

 sea-level) the moraine sand and boulder-clay reaches 30 to fiO feet 

 in depth. The deposits consist largely of calcareous and also 

 siliceous sand, bearing a great many large angular blocks, together 

 with smaller ones, partially rounded-off, polished and striated. The 

 deposits in the mounds overlying the gravel beds of second glacia- 

 tion near Killwangen, between Zurich and Baden, which I also 

 examined, present similar features, but the characteristic feature 

 which distinguishes all these deposits from those of the second 

 glaciation consists in the blocks and pebbles, viz. grey, red, and 

 black limestone, green sandstone with black spots, derived ex- 

 clusively from the Glarner Alps, viz. from the Linth watershed, 

 the granites and other rocks of the Julier Alps and the Vorder- 

 Ehine, viz. of the Rhine drainage area, being entirely absent. This 

 fact affords substantial proof that in Upper Pleistocene times, viz. at 

 the time of the third glaciation, the connection between the Ehine 

 and Linth systems was already severed by the saddle thrown up 

 by the Setz and Tamina at Sargans. The Linth glacier, properly 

 speaking, did not advance beyond Baden ; on receding it halted at 

 Killwangen, and subsequently was for a long time stationary near 

 Zurich, as evidenced by the terminal moraine walls which are so 

 characteristic of that town. 



Conclusion. — After the great folding, thrusting, and raising of the 

 Alps in Miocene and Pliocene times, coinciding with the formation 

 of the principal Alpine valleys, and accompanied by great climatic 

 changes, we have, therefore : — 



(1) A first glaciation and filling up of the valleys by glacial 

 deposits, the limit of glaciation or terminal moraine in the North 

 of Switzerland being a curve between Zurich and the Khine at 

 Kaiserstuhl and Irschel, and the axis of the main glacier pointing 

 in the direction of Waldshut, the present confluence of the Aai'e and 

 Ehine systems. 



(2) A second glaciation, which, in the North of Switzerland, 

 spread to the foot of the Jura, to Basle, and the Ehine. 



(3) A third glaciation, which did not spread beyond the limits of 

 the first, viz. to within 10 miles below Zurich on the one hand, and 

 to the Ehine as far as Schaffhausen on the other, while the tongues 

 of the Eeuss glacier advanced to within about six miles of Turgi 

 and Aaran, the Aare glacier to within ten miles of Olten, and the 

 northern tongue of the Ehone glacier extended along the base of the 

 Jura to about four miles beyond Soleure in the present Aare valley. 



