Vol. 58.] HANGING VALLEYS IN THE ALPS AND HIMALAYAS. 707 
There are, however, three important facts which bear directly on 
the point at issue. The first of these is the striking manner in 
which many of the lateral tributaries enter the Ticino by gorges 
which point up stream. It was when seeking a solution of this 
curious phenomenon, that the idea of an elevation of the upper end 
of the district first occurred to me as the only possible explanation 
of the tilting of these gorges from their original vertical position. 
Another significant fact is the manner in which the drainage of 
the Val Piora has collected at its lower end to form Lago Ritom; | 
and the third is the past history of the drainage of the Val 
Piumogna, opposite Faido. 
The question of the origin of the group of lakes in the neigh- 
bourhood of the Val Piora is one which I must leave till another 
occasion; but it seems probable that, should an elevation of the 
upper end of the Val Ticino have taken place as postulated, there 
would be a tendency for the drainage to collect at the lower end 
of the Val Piora, until such time as a gorge should be cut 
down to a sufficient depth to drain off the accumulated water. 
That this result would be indefinitely delayed may be expected, 
when we remember that, on the first formation of the lake, all the 
transported fragments by which the work must be effected would 
be deposited at the upper end of the lake to form the delta on which 
the farm-buildings of Campo now stand, and only clear water would 
lap over into the old channel: the resulting fall has gradually cut 
back a gorge in the old valley below, but has not, as yet, appreciably 
affected the level of the lake above. 
The direction of the ancient drainage of the Val Piumogna is 
another instance bearing on this question. In former times, the 
river appears to have drained westward from the hamlet of Dalpe by 
Prato, entering the Ticino where Morasco now stands, being headed 
off by the rocks of Monte Piottino so as to enter the Ticino up 
stream. This old depression is a conspicuous feature, and was the 
line followed by the old Roman road which climbed over Monte 
Piottino, past Prato and Cornone, to avoid the river-gorge below. 
After the elevation, the river was diverted to the east at right 
angles to its former course, and now falls in a series of cascades 
into the Ticino opposite Faido; the relics of the lake thus formed 
are seen in the deposit of alluvium in the valley above the fall.’ 
The questions now remain, When did this elevation take place ? 
and to what was it due ? 
One point seems perfectly clear, namely, that it originated at all 
events before the last occupation of the valley by ice. ‘This is 
shown, not only by the polished sides of the overdeepened portion of 
the main valley, but also by the rounded edges of the hanging 
valleys where these debouch into the Valle Leventina. The steep 
rock-walls on the western bank of the Ticino below Faido, however, 
are deceptive in this respect: the smooth slabs over which the 
1 See K. von Fritsch, ‘ Geognostische Karte des Sanct Gotthard’ Beitr. z. 
Geol. Karte d. Schweiz, vol. xv (1873). 
30 2 
