706 PROF. GARWOOD ON THE ORIGIN OF SOME [ Nov. 1902, 
main valleys, especially perhaps above Airolo where the softer 
Jurassic beds have been let in. 
A glance at the accompanying map (Pl. XXXVI) shows that, 
although the valley between Biasca and Giornico is fairly open, 
this is by no means the case above the latter village; and, instead 
of the trough-like character described by Prof. Davis as typical 
of a valley overdeepened by ice, we have exactly the features 
shown in fig. 1 of his paper’ as characteristic of a water-cut valley, 
spur after spur overlapping in the distance, while the river winds 
sharply between its rocky walls. Thus, through Monte Piottino, 
the valley makes a double rectangular turn, necessitating two of 
the famous spiral tunnels above Faido, and similar overlapping 
profiles occur near Lavorgo, below Faido (see Pl. XX XVII, figs. 1 
& 2, and explanation). Between these points, immediately opposite 
Faido, lies the hanging valley of Piumogna. Higher up again, nearer 
Airolo, we have two undoubted river-gorges, near Madrano and 
Brugnasco respectively, the former being so canon-like in character 
that for both road and railway it has been necessary to resort to 
tunnelling (Pl. XXXIX, fig. 1). 
We see, then, that the Valle Leventina shows all the features 
typical of a valley excavated by water, especially as regards the 
steeper basal trench represented in fig. 3 of Prof. Davis’s paper.” 
The more open portion, near Biasca, presents no features inex- 
plicable by ordinary river-erosion, and the width of its floor is 
undoubtedly increased by the deposition of shingle washed down 
from the upper valley, giving a much flatter character to the section 
than it would otherwise possess. The only abnormal features, 
therefore, are the hanging valleys, and these occur equally in the 
upper portion of the Valle Leventina, where (as we have seen) 
sections of the basal trench of the main valley between them are 
undoubtedly river-gorges as shown above. There is, then, no direct 
evidence that the overdeepening of the main valley, which has 
resulted in the production of the discordant lateral valleys, is due 
to erosion by ice; and it remains to account for the presence of 
these valleys by the ordinary process of river-excavation. 
Now, all that would be required to produce the discordance in 
question would be an acceleration of the main Ticino River without 
a corresponding acceleration of its tributaries. This would im- 
mediately be produced were an elevation to take place at the upper 
end of the Val Ticino, whereby the grade of the valley should be 
perceptibly increased, while the lateral valleys were merely tilted 
sideways. That such an elevation has taken place I have, for some 
time past, considered as the only explanation possible of certain 
other phenomena in the district. Most of these do not directly 
bear on the subject in hand, although I think that the hanging 
valleys are but incidents connected with much larger problems of 
drainage on the southern side of the Alps, of which the formation 
of the Italian lakes constitutes an integral part. 
‘ «Glacial Erosion in the Valley of the Ticino’ Appalachia, vol. ix (1900) 
p. 142. 2 Ibid. p. 146. . 
