228 
SCENERY OF SWITZERLAND. 
At present the Aar makes a sharp turn to the west 
at Waldshut, where it falls into the Rhine, but there 
is some reason to believe that at a former period, 
the river continued its course eastward to the Lake 
of Constance, by the valley of the Klettgau, as is 
indicated by the presence of gravel beds containing 
pebbles which have been brought, not by the Rhine 
from the Orisons, but by the Aar from the Bernese 
Oberland, showing that the river which occupied the 
valley at that time was not the Rhine but the Aar. 
It would seem also that at one time the Lake of 
Constance stood at a considerably higher level, and 
that the outlet was, perhaps, from Friedrichshafen 
to Ulm, along what are now the valleys of the 
Schussen and the Ried, into the Danube.* 
The River Aach, though a tributary of the Rhine, 
still derives its head-waters from the valley of the 
Danube. A part of the water of the Danube sinks 
into fissures in the Jurassic rocks at Immendingen, 
and makes its appearance again as copious springs 
at Aach, from whence they flow into the Lake of 
Constance near Rudolphzell. 
Thus the head-waters of the Rhone appear to 
have originally run between Morges and Lausanne 
Du Pasquier, Beitr. z. Geol. K. d. Sckw., L. XXXI. 
