Vol. 58.] HANGING VALLEYS IN THE ALPS AND HIMALAYAS. 705 
of the main-valley wall below the level of the hanging valleys ; 
and (2) the absence of 
‘ overlapping profiles, entering the valley from one side and the other alternately, 
and concealing the more distant parts of the valley-floor.’ ! 
The first of these arguments does not by itself afford any evidence 
of overdeepening by ice, as we have plenty of instances of river- 
gorges with inaccessible sides and subparallel walls. No one, for 
instance, imagines that the canons of Colorado or the gorge of the 
Via Mala owe their origin to overdeepening by ice; and this 
Prof. Davis would be the first to admit. It is, therefore, on the 
second statement—that the characteristic ‘ crossing spurs’ are absent 
from the Val Ticino—that the ice-excavation theory relies, sup- 
ported by the presence of the hanging valleys and the steeper grade 
of the main-valley walls beneath. 
Now, the hanging valleys described by Prof. Davis are all situated 
a short distance above or below Biasca, and his description of the 
valley’s characteristics is entirely drawn from this portion of the 
Val Ticino. The valleys below Biasca are complicated by the results 
of the additional drainage from the Val Blenio; and as the portion 
above Biasca contains three of Prof. Davis’s typical valleys, namely, 
the Val d’Ambra, the Val Nadro, ind the Val Cramosina, I propose to 
confine myself to a description of the features of the Valle Leventina 
between Airolo and Biasca. For here we have but one main valley, 
running between two parallel ranges, which receives no sudden 
access of drainage at any portion of its course, the conditions under 
which any of its features were produced being consequently the same 
throughout. 
Ii we examine the entire length of this valley, we find that the 
hanging valleys are by no means confined to the three just above 
Biasca, before mentioned, but occur at intervals right up to Piotta, 
3 miles below Airolo, where the torrent of La Foos” plunges from 
the lake of Ritom in the Val Piora, by far the largest hanging valley © 
in the district. Farther up again, the Val Tremola, draining the 
St. Gotthard Pass, though partly cut back, comes under this category ; 
and higher still, in the Val Bedretto, the trench-like appearance of 
the valley and the precipitous character of the lateral streams are 
very marked features for a considerable distance. Among others, 
I may cite the Val Piumogna opposite Faido, and the Val Chironico 
_ above Giornico. Both of these are every whit as discordant in their 
relation to the Valle Leventina as those mentioned near Biasca, and 
whatever theory we adopt as to une mode of formation of one must. 
apply equally to all. 
I do not wish here to discuss the faulted character of the valley- 
floor above Faido, as I do not think that this has influenced the 
formation of hanging valleys, except to hasten the deepening of 
1 See Prof. Davis’s paper, ‘Glacial Erosion in the Valley of the Ticino’ 
Appalachia, vol. ix (1900) p. 142. 
2 Misprinted ‘ Foss’ on the section and map, Pl. XXXVI. 
Q.J.G.8. No. 2382. 3.0 
