Dr. Du Riclie Preller — TJiree Olaciations of Switzerland. 29 



nagelfluh. Upon the sub-tropical molasse age, essentially one of 

 slow accumulation and spreading of clay, sand, and mud, followed in 

 early Pliocene times the formation of the Alpine and sub- Alpine 

 valleys, partly as the effect of thrusting, folding and upheaving of 

 the Alps, partly by the action of Alpine rivers, whose erosive power 

 had become greatly enhanced by the greater fall of the upheaved, 

 and, moreover, more or less denuded Alpine slopes. It may, there- 

 fore, be assumed that by the end of this Pliocene period of erosion, 

 as distinguished from the Miocene period of accumulation, the Alps 

 and the principal Alpine, as well as sub-Alpine, valleys presented, 

 broadly speaking, the general outlines which they exhibit now. 



First Glaciation. — The valley-making of Pliocene times was 

 accompanied by a gradual drop of temperature, due probably to an 

 increase of precipitation, viz. of snow and rainfall in the Alps raised 

 considerably above their former level; and so great was this climatic 

 change that the latter part of the Pliocene age was marked by a 

 general advance of the Alpine glaciers and a first glacial invasion of 

 the Swiss lowlands. This first glaciation of Pliocene, viz. Tertiary 

 age, is evidenced by the so-called hollowed-out or " locherig " 

 nagelfluh, which is quite different and distinct, not only from the 

 molasse or Miocene conglomerate bearing the same name, but also 

 from the gravel deposits of subsequent glaciations. The qualification 

 of "hollowed-out" (locherig) was first given to this nagelfluh by 

 Escher von der Linth, owing to the holes left in the clayey and cal- 

 careous cement by pebbles which had been decomposed and washed 

 out by chemical action. Mousson, Escher von der Linth, and 

 Gutzwiller recognized it as a glacial deposit much more recent than 

 the molasse. Wettstein, writing in 1885,^ did the same, but included 

 it in the later (then first) glacial period ; Prof. Heim, as recently as 

 1891,^ speaks of it tentatively as perhaps belonging to an older 

 glaciation. But as early as 1885 and 1886, Prof. Penck ^ and Prof. 

 Bruckner * had recognized three distinct glaciations in the Bavarian 

 and Austrian Alps, and had pointed out the close analogy between the 

 " Deckenschotter " or sheet-gravel of those Alps, and the Swiss fluvio- 

 glacial deposits;^ and it was not till quite recently, viz. 1891-92, 

 that Swiss geologists, and first among them Dr. Du Pasquier, 

 took the plunge and adopted the same view. Of the various deposits 

 of this Pliocene nagelfluh which 1 have examined, there are more 

 especially two very instructive ones, one on the Utlibei'g near Zurich, 

 and the other near Baden, about fourteen miles below Zurich. As 

 is seen from the diagram, the summit of the Utliberg is formed by 

 Pliocene hollow nagelfluh, which rests on moraine or boulder-clay, 

 and this in its turn rests unconformably on Miocene molasse and 

 nagelfluh. An erratic block of Miocene nagelfluh, which was found 

 in 1883 imbedded in the moraine and below the hollow nagelfluh, 



1 A. "Wettstein, " Geologie von Zurich, und Umgebung, 1885." This gifted young 

 geologist lost his life on the Jungfrau. 



2 Naturf. Gesells. Neujahrsblatt, 1891. 



3 Vergletcherung der Deutschen Alpeu, 1885 ; Der Alte Eheingletscher, 1886. 

 * Vergletcherung der Salzach Gebietes, 1886. 



° Fluvio Glaciale Ablagerungen der iSfordschweiz. Geol. Karte Schweiz, 1891. 



