Vol. 52.] DEPOSITS, ETC., IX SUBALPINE SWITZERLAND. 575 



the narrow Baden defile, which, near the apex of the two V-shaped 

 passages, is even now not more than 30 metres in width, the valley 

 at the lake-level near Ufenau is at least 3 kilometres broad, and 

 hence the removal of the old saddle cannot be attributed solely to 

 the erosive action of the Preglacial Linth, but must be, in part, 

 the effect of a subsequent subsidence of the old valley-floor, as will 

 appear in the sequel. 



Proceeding now to the reconstruction of the Zurich valley 

 •(figs. 1 & 12, pp. 558, 577) as it appeared at the advent of the first 

 glaciation, we have to trace the lowest points at which the solid 

 rock appears, as marking the old valley-floor, especially where the 

 rock is directly overlain by Deckenschotter. 



Beginning at the confluence of the Limmat and Aare, near Turgi, 

 we find the solid rock practically at river-level on the left bank of 

 the Aare at Lauffohr, exactly at the junction, that is at contour 332. 

 Thence proceeding up the Limmat valley, we strike it again for 

 about a hundred metres at the river-level about halfway between 

 Turgi and Baden, at contour 340 ; then at Baden, near the lower 

 end of the basin, at contour 351 ; and again at Wettingen, near 

 the lower and upper viaducts, at contours 358 and 362 respectively, 

 both the Lower Baden and Upper Wettingen exposures being, as 

 already shown, directly overlain by Cavernous Nagelfluh. The first 

 section of the old valley-floor thus has a fall of 30 metres in 8*5 

 kilometres, or 3*5 metres per 1000, equal to 1 in 286, or roughly 

 1 in 300. If we assume this as the uniform fall also for the upper 

 sections, the old valley-floor was near Hongg at contour 412, a few 

 metres lower than the Deckenschotter exposure described, and about 

 15 metres above the present river-level ; near Zurich at contour 433, 

 -or 24 metres higher than the present lake ; near Kiissnacht at 

 contour 451, or 42 metres higher than the lake, and about 50 metres 

 lower than the Deckenschotter deposit in the Kiissnacht ravine ; 

 near Au at contour 483, or 74 metres above the present lake-level ; 

 near Altschloss at contour 500, or 91 metres higher ; and near 

 Richterswil — that is, on a level with the Marine Molasse bank of 

 Wollerau — at contour 518, or 109 metres above the present lake- 

 level, the distance of this point from Turgi being 52 kilometres. 

 The Marine Molasse bank of Wollerau, at contour 518, marks the 

 confluence of the Preglacial Linth and Sihl, and therefore approxi- 

 mately also the then level of the passage already eroded in the 

 Ufenau saddle, whose highest points, namely, Ufenau and Liitzelau, 

 must, however, have been as yet at a higher level. If, proceeding 

 from this point upwards, we assume the gradient of the Preglacial 

 Linth valley to be the same as in the lower sections, the floor at the 

 junction of the Linth and western Rhine valleys near Wesen, or the 

 present Walen Lake (distance 25 kilometres), must have been at 

 contour 605, or 182 metres above the present level of that lake, 

 while at Glarus, or 10 kilometres farther, it was at contour 640, 

 that is, 159 metres higher than the present valley-floor at that 

 point. The same gradient prolonged from Wesen for a distance of 

 30 kilometres through the Walen lake-basin to Sargaus, the point 



