i 5 o SCIENCE PROGRESS. 



of the zones of Mont Blanc and Monte Rosa; (2) the 

 existence of the hypothetical " Double- Fold of Glarus " 

 which has been assumed to explain the occurrence of older 

 beds over newer ones in the Todi-Windgallen group ; and 

 (3) the origin of the Prealpes and the possible former 

 existence of the " Vindelecian Mountains". 



The " Double-Fold" and Dr. A. Rothpletz's alternative 

 explanation (1) have been clearly summarised by Dr. 

 Hume in a recent number of " Science Progress," so that 

 the question need not be further considered here. 



I.— THE STRUCTURE OF THE PREAEPES. 



The Prealpes (of M. Renevier) or the zone of Chablais 

 (of Diener) is one of the smallest of the Alpine zones, but 

 it has given rise to much discussion. The zone forms a 

 narrow band which runs from the western end of the 

 Wallensee to the great bend at the eastern corner of the 

 Lake of Lucerne. It includes the southern slopes of the 

 Riei and Pilatus, and the whole of the eastern end of Lake 

 Thun. Further west it expands to include a broad tract of 

 country, comprising the Stockhorn and other mountains to 

 the south of Freiburg, and the district of Chablais to the 

 south of the Lake of Geneva. The zone is composed of 

 rocks ranging in age from the Trias to the Oligocene, the 

 characters of which are very different from those of the 

 zone to the south, or the main Limestone Alps. They 

 approximate much more closely to those of the "Zone du 

 Brian^onnais," which is three zones to the south. The 

 occurrence of this isolated mass, which seemed so different 

 from and independent of its neighbours, on the north flank 

 of the Limestone Alps, appeared so anomalous that many 

 efforts to explain it have been made. The best known of 

 these is that of M. Schardt in a paper (2) published at 

 the end of December, 1893. He denies the obvious ex- 

 planation that the remarkable differences between the 

 lithological character of this zone and that of the next to 

 the south may be due to deposition under different con- 

 ditions. He says there is no evidence for this, and the 



