266 Professors Heim and Penek — Glaciers of the Isar andLinth. 



Of the three grounds, which, according to Penek, support the 

 glacial origin of the Lakes of Amnier, Wuerm, Rieg, and Staffel, only 

 the two former are applicable to the Lake of Zurich, and the other 

 large lakes of the Swiss Alpine borderland. But just as little as in 

 the first case, the position of the lakes in the area of glacial deposits, 

 and, in the second, the character of the lake valleys as produced by 

 erosion, can be disputed, even so little can the age of the lakes be 

 brought forward as a proof of their origin. 



Whilst namely, on the one hand, the gravel deposits indicated by 

 II. a and II. b are only thus locally and sporadically developed, so that 

 no conclusion can be at present arrived at as to their former connection, 

 it can neither be proved that the lake valleys are depressions in a 

 former covering of diluvial Nagelfiuh, nor that the lake-basins repre- 

 sent hollows in a gravel formation corresponding to I. b. There is 

 thus nothing to add to our information respecting their Quaternary, 

 i.e. Glacial age. But, on the other hand, the Nagelfiuh of the Au 

 represents a probably very ancient deposit, which, by its delta struc- 

 ture, proves the existence of the Lake of Zurich already previous to 

 the commencement of the last glaciation, so that the lake cannot be 

 attributed to its action. At the same time, the position of the rock- 

 terraces of the declivities of the valley afford decisive proof of dis- 

 locations which affected the lake valley and produced the basin- 

 shaped depression in it. Penek holds with Heim and Wettstein that 

 there is undeniable evidence of the influence of dislocations in the 

 formation of the basin of the Lake of Zurich, but he is never- 

 theless of the opinion, that with a more thorough investigation of 

 the Swiss Quaternary gravel deposits, it may perhaps be found pos- 

 sible to discover a parallel between the deposits named I. b and II. b in 

 the two areas respectively, and he holds the view that the lake-basin 

 originally produced by dislocation may be to a greater or lesser degree 

 excavated by glacier action. Heim also does not question the fact of 

 a certain, though relatively small, amount of the scooping out of the 

 lake-basin being due to the glacier. 



Penek holds that to re-excavation may very probably be attributed 

 the formation of the lakes of the Glatt valley, of the Greifen Lake 

 and Pfaffikon Lake, in the same way as in the case of Rieg Lake and 

 Staffel Lake, whilst Heim is disposed rather to explain the origin of 

 these two lakes of the district of the Glatt valley to the blocking-up 

 action of moraines. 



There is, therefore, no real difference of opinion between us 

 touching the Lake of Zurich and the Lakes of the Bavarian high- 

 lands, either as regards the facts or the conclusions from them ; and 

 as in the present case, so also does it often happen, that by a more 

 exact conjoint examination, differences become of much less import- 

 ance than they appear to be from a distance. 



