DAVIS : GLACIAL EROSION. 
287 
Fi°r. 5 
True-scale cross-section 
of the Lauterbrunnen valley. 
Inn and of the Aar. Lakes Thun and Brienz receive numerous 
cascades from hanging valleys that stand high above the water 
surface. The valley of Lauterbrunnen also affords a conspicuous 
illustration of a deep bottom trough enclosed by high basal cliffs 
that rise to the edge of more open upper slopes; the celebrated 
Staubbacli fall is the descent of a small lateral stream from its lofty 
hanging valley (see extract from an article by Wallace, cited 
below), and the picturesque village of Miirren, M, Fig. 5, stands 
on the flaring slope or Tlialstufe of 
the preglacial valley, just above the 
great basal cliff of glacial origin. A 
mile or so south of the village of 
Lauterbrunnen, the Trummelbach, 
T, Fig. 5, descends the precipitous 
eastern wall from a hanging valley 
whose floor is hundreds of feet above 
that of the Liitschine ; it is roughly 
sketched in Fig. 6. Although the 
lateral Trummelbach brings a large volume of water to the main 
valley, it descends by a very narrow cleft in the rock face, a trifling 
incision in the valley wall; while the main valley, whose trunk 
stream did not seem to be more 
than five times the volume of its 
branch, is half a mile or more 
broad, wide open and flat-floored. 
The cross-section of the main 
valley is over a thousand times as 
large as that of the lateral cleft. 
Such a disproportion of main 
valley and lateral cleft is entirely 
beyond explanation by the in¬ 
equality of their streams ; and for 
those who feel that they must 
reject glacial erosion as the cause 
of the disproportion, there seems 
to be no refuge but in ascribing 
the main valley to recent down- 
faulting : a process that can hardly 
be called on to follow systematically along the floors of the larger 
glaciated valleys of the Alps, and to avoid the non-glaciated valleys 
and the mountain ridges. 
Fig. 6. 
Diagram of the gorge of 
the Trummelbach, Lauterbrunnen 
valley. 
ft 
4 
