386 DE. C. S. DtT KICHE PKELLER ON PLTTVIO-GLACIAL [Aug. 1895, 



to Heer, we must therefore assume that during the first interglacial 

 period the rate of deposition, and hence that of erosion, was 40 

 times greater than it is in our own day. As has been pointed out, 

 the formation of the Uznach lignite-deposits must have taken 

 more than 6000 years. Hence it is reasonable to infer, contrary 

 to the hitherto commonly accepted opinion, that the first interglacial 

 period was the shorter, and the second the longer of the two. 



However that may be, the Austrian and Bavarian Decken- 

 schotter, the Swiss Cavernous Nagelfluh, the French ' alluvions 

 anciennes,' and the Italian ' alluvioni antichi ' constitute at the 

 base of the Alps a belt of fluvio-glacial deposits which, being the 

 indirect product of ice, are evidence of a first or Pliocene glaciation; 

 while the lignites formed between two alternations of the younger 

 morainic deposits, such as the lignites near Sonthofen in Algau, 

 Bavaria, in the JNorth of Switzerland, in the Kander Valley near 

 Thun, those near Chambery in Savoy, and those near Leffe and 

 elsewhere in the North of Italy, besides the contemporaneous 

 upper gravels, constitute another belt as evidence of the two sub- 

 sequent Pleistocene glaciations. 



For the rest, a careful and unprejudiced study of glacial and 

 interglacial deposits in the Alps leads to the irresistible conclusion, 

 already pointed out in the paper on the three glaciations (Geol. 

 Mag. 1894), and also established by Dr. L. Du Pasquier and others, 

 that every general glaciation marks a period of filling up, and every 

 interglacial period marks a period of erosion of valleys ; in other 

 terms, that such erosion is mainly due to fluviatile, and not to glacial 

 action. 



Discussion". 



Prof. Bonnet expressed his sense of the value of the paper. He 

 had had the opportunity, through the kindness of Dr. Preller, of 

 examining several of the sections described in the paper, and could 

 corroborate many of the statements made. There appeared to be in 

 the neighbourhood of Zurich three separate morainic deposits with 

 great intervening masses of stratified gravel ; and he had been 

 surprised to see how large an amount of erosion must have taken 

 place between the deposition of the Cavernous Nagelfluh on the 

 Uetliberg and that of the morainic deposits, some 1200 feet below it, 

 about Zurich. But he thought that at present we could hardly attempt 

 to correlate the Swiss and the British Glacial deposits. The former, 

 however, were of peculiar value, because there could be no doubt 

 that all were supra-terrestrial. 



Mr. Monckton thought that the materials for the newer gravels 

 of the Zurich district had been largely derived from older gravels or 

 conglomerates of the Uetliberg class in the same area, and that the 

 Uetliberg conglomerate derived its materials from the older con- 

 glomerates of the Bigi. In the same way in the South of England, 

 materials had been passed on from older to newer gravels over and 

 over again. In the Zurich district there was evidence of con- 

 siderable differential elevation or depression since the formation of 



