350 Dr. C. S. Du Riche Preller — Alpine, Lowland, and 



1. Lalces Pfaffikon and Greifensee (Sheet No. 3, Fig. Y) lie in shallow 

 depressions of the Glatt Valley area and are twin lakes, heing fed by 

 the Aa as principal affluent, which, on emerging from Greifensee, 

 takes the name of Glatt. Both have lost much of their former size, 

 Greifensee having shrunk to less than half its former extent. They 

 are both banked by moraine, and are the remnants of lakes formed 

 during the recession of the Linth Glacier, which, probably augmented 

 by a branch of the Rhine Glacier, filled the Glatt Yalley and advanced 

 to within a few miles of the Rhine at Eglisau. The Glatt Valley 

 presents a noteworthy feature in that, after the Linth had been 

 deflected back to the Zurich Basin after the last glaciation, it became 

 a dried-up valley whose floor lies now from 30 to 50 metres higher 

 than that of Lake Zurich. The same phenomenon characterizes the 

 neighbouring valleys of the Rhine drainage area, such as the Thur 

 and Toss Yalleys, whose great width is altogether disproportionate to 

 the size of the present affluents of the Rhine, and which must have 

 been eroded by rivers of much larger volume. 



2. Lakes Baldegg, Hallwil, and Sempach (Sheet No. 3, Fig. Y). — The 

 first two of these are twin lakes, being fed by the same river, the Aa, 

 while Lake Sempach, in a neighbouring parallel valley, has for its 

 principal affluent the Suhr, both rivers being tributaries of the Aare. 

 The three lakes present precisely similar features, the first two 

 occupying shallow basins in the Seetal Valley, while the third lies in 

 a similar depression of the Suhr Valley. All three have shrunk to 

 two-thirds of their former size, and the valleys, as also the contiguous 

 parallel ones of the Wyna and "Wigger, are disproportionally wide 

 in relation to the small rivers. Like the valleys of the Rhine 

 affluents, they must have been eroded by rivers of much larger 

 volume and erosive force, or may have been occupied for a long 

 period by shallow lacustrine expanses ; possibly, here, as there, the 

 indirect action of ice by pressure also contributed to give them the 

 flat-dome lines of the Molasse formation. All three lakes lie in 

 the area of the Aare "Glacier and are banked by moraine; hence they 

 must have been formed during the retreat of that glacier. 



3. Lalces Lowertz and Sarnen (Sheet No. 1, Fig. I, and Sheet No. 4, 

 Fig. VII) properly form part of the Lake Lucerne system into which 

 they drain. Lake Lowertz, a remnant of the Reuss when the whole, 

 or part of it, flowed along the northern base of Rigi, now discharges, 



