THE CENTRAL PLAIN. 
41 
tinuous cold, but that it was interrupted by more 
genial periods. 
Fig. 82 represents a section across the valley of 
the Aar, from l.euggern to Klingiiau, a short distance 
above Coblenz. It is a general character of the 
Upper terraces to be capped by loam or “Loess,” 
the deposit of ancient floods before the present river 
valleys had been cut down to their present depths. 
Most of the river valleys originated before the 
Glacial period, and the main erosion seems to have 
Fig. 82. — Section of the Valley of the Aar. 
been completed before the second Ice age. That 
they were occupied by glaciers during the second and 
third Glacial periods (see Map, vol. 1. p. 136) is proved, 
as already mentioned, by the existence of numerous 
terminal moraines crossing the valleys, and lateral 
moraines lining the hills along the principal river 
Valleys; as for instance the Aar, especially from Thun 
to Bern, the Subr from Sempach to Wittwyl, the Aar 
from the Baldegger See to Lenzburg, the Reuss from 
Klein Dietwil below Lucerne to Mellingen, the Valley 
