LAKES. 
251 
Firstly, the lakes of the Jura, — those of Neuchatel, 
Bienne, and Moral, which occupy synclinal valleys. 
Secondly, those of Hallwyl, Baldegger, Sempach, 
Greifen, etc., which are moraine lakes, the dams at 
the lower ends being moraines. 
Thirdly, those of Constance, Zurich, Walen, Zug, 
Lucerne, Thun, Brienz, and Geneva, some of which 
are indeed partially dammed up by ancient moraines, 
but which are partly at least due to the lower ends 
of the valleys having risen relatively to the rest. 
Dr. F. A. Forel has suggested * that this sub- 
sidence of the Central Alps also throws light upon 
the former extension of the glaciers. The present 
snow-line is at a height of say 2600 metres. If we 
assume the subsidence to have been 500 metres 
(which seems the minimum), and suppose that 900 
metres have been since removed from the whole sur- 
face, certainly no exaggerated estimate, this would 
bring the snow down to the present line of 600 metres, 
which would involve a great extension of the Firn, 
and consequently of the glaciers. He considers that 
an elevation of 900 metres would bring the glaciers 
of the Rhone down again to the Lake of Geneva. 
The theory deserves careful study but is open to 
* Le Leman. 
