Until very recently it was thoroughly recognised that in post- Tertiary, viz., Pleistocene or Diluvial times, there occurred in Switzerland, as elsewhere, two glaciations which covered the Alps and the greater part of the Swiss lowlands, and between which intervened a genial or interglacial period. The repeated advance of Swiss glaciers was first established by Escher von der Linth and Heer, more especially upon the evidence of the lignite slate deposits near Durnten and Wetzikon, which fringe the edge of what was at one time the Limmat and is now the Glatt valley, to the N.E. of Zurich, and were formed during the interglacial period referred to.