204 
SCENERY OF SWITZERLAND. 
of the Aar and the Reuss into lakes — the two branches 
of the Lake of Lucerne known as the AIpnach See 
and Uuier See. The Bays of AIpnach and Klissnach 
are in fact a continuation of the valley of the Sarnen 
Aa, which forms the Lake of Sarnen. The Bay of 
AIpnach lies in a synclinal valley between two cre- 
taceous ridges which unite further west to form the 
Burgenberg. Several of the smaller bays, as for in- 
stance those of Langensand and Winkel, are due to 
the existence of comparatively soft and destructible 
strata. Ihe Bay of Uri is a transverse valley, part 
of the course of the Reuss. 
The Buochs-Brunnen-stretch is a trough, — perhaps 
the old course of the Engelberger Aa, when it joined 
the ancient Reuss at Brunnen and continued with it 
by Schwyz and Zug; the portion near Brunnen is, 
moreover, in a synclinal. The Wilggis-Vitznau basin 
on the contrary is a “combe.” The Mollasse (Nagelflue) 
of the Rigi slopes to it on the north, and on the south 
it is bounded by the fractured arch of the Biirgen- 
berg. The Bay of Lucerne is excavated in Mollasse, 
and is probably the most recent portion of the lake.* 
The Lake of Zug has somewhat the form of an 
hour-glass, owing to a bed of hard puddingstone 
which crosses it obliquely to the north of Immensee. 
* Rtitimeyer, Dcr Rigi, 
