220 Dr. C. S. Du Riche Preller — Zonal Lake Basins. 



entirely in the Molasse formation. The conclusions which I drew 

 from these facts as to the age and origin of these basins having, 

 since then, been confirmed by further evidence, it will not be without 

 interest to return to the subject. 



I. The Lake Basins. 



The following table and the accompanying longitudinal sections, 

 pp. 216-17, Sheets 1 and 2 (Figs. I-V), outline the salient features 

 of the five zonal basins, to which are added (Pig. VI) those of the 

 lakes of Neuchatel and Bienne because, although not zonal in respect 

 of the other lakes, they present certain features common to all of them. 

 All the dimensions are given in metric measure so as to correspond 

 to the Swiss contour map from which the sections are plotted. 



Prom the table and the sections it will be seen that all the lakes 

 have lost at least one-third of their former length. At the upper ends 

 the shrinkage is due to filling up by post-Glacial fluviatile alluvia, 

 viz. mud, sand, and gravel; in the Rhone and Rhine valleys to some 

 extent also by superficial deposits of loess borne by the Pochn, while 

 at the lower ends it is largely the effect of banking by the post-Glacial 

 deposits of rivers which discharge into the lake valleys more or less at 

 right angles immediately below or above the present outflow of the 

 lakes. The only exception is the Lake of Constance, which at its 

 lower end lies entirely in a moraine basin, the shrinkage being due to 

 moraine material retransported by the Rhine. 1 



A peculiar and very complex case is that of the Lake of Lucerne, 

 ante, p. 218, which, as shown in Pig. VII, is composed of five, and, 



1 In the other lakes the fluviatile bars were formed by the following rivers : 

 in the Lake of Zurich,' by the Sihl ; in the Walensee (an old branch of the 

 Bhine), by the Linth ; in the Lake of Lucerne, by the Emme, which, however', 

 only deflected the Beuss instead of barring the lake ; in the Lake of Thun, by 

 the Kander ; in that of Brienz, by the Lutschinen delta of Interlaken ; in 

 the Lake of Geneva, by the Arve ; and in the Lakes of Neuchatel and Bienne, 

 by the Aare. 



