708 PROF. GARWOOD ON THE ORIGIN OF SOME [ Nov. 1902, 
rivulets cascade, which at first sight seem to point to great glacial 
erosion, are in reality due to planes of foliation in the gneiss. 
This is proved by the manner in which many of these smooth 
surfaces pass under the overlying slabs, while the truncated edges 
of these beds are sharp and angular, although they face up stream. 
In many cases, also, as under Calonico Church, the recent rock-falls 
from the surface of these slabs can be seen below. 
This elevation may possibly have been initiated in pre-Glacial times 
as a final stage in the orogenic uplift in the late Pliocene Period. 
I, however, incline to the belief that the hanging valleys were 
produced during the warmer inter-Glacial Periods, the existence of 
which in the Alps, first suggested fifty-five years ago by Collomhb, has 
been now clearly demonstrated by the researches of J:.mes Geikie, 
Penck, Blaas, Boehm, and others. Thus Prof. Penck! attributes an 
excavation of 720 feet in the valley of the Iller to river-erosion, 
during the mild period antecedent to the last advance of the Iler 
Glacier. 
So far as I am aware, no lignite-deposits of this age have been 
recorded from the Val Ticino; but should any occur, I would expect 
to find them on the upper benches above Faido, between Mairengo 
and Calpiogna, and on the corresponding plateau between Dalpe and 
Prato. Possibly the lake-deposits mentioned above might contain 
remains of this inter-Glacial flora, while the presence of a fragment 
of a lower bench at 816 metres may indicate a succession of at least 
two former valley-floors. 
One fact which seems to be more and more clearly established 
every year, is the tendency shown by all glaciated districts to 
undergo elevation as their covering of ice melts away. I need only 
recall the raised beaches of Spitsbergen, Franz-Josef Land, Nor- 
way, and North America, leaving out of account for the moment the. 
Himalayas and the Alps themselves. One of the most interesting 
points recorded in a recent report of the Norwegian Geological 
Survey, is the coincidence of the greatest post-Glacial rise with the 
area of the greatest depression below the axis of the inland ice.’ 
If this rise be accepted also for the Alps, after the maximum period 
of glaciation was passed, we have at once a solution of the problem 
of the hanging valleys. As the ice melted back, torrents of water 
would be discharged from the fronts of the retreating glaciers, 
and, as the country rose, the main river would rapidly deepen its 
valley, while the lateral valleys would not only remain at their 
former grade, but would also continue to be occupied for some time 
longer by ice—a fact well illustrated in the Alps nowadays. The 
hanging valleys thus initiated would be prevented from immediately 
establishing an accordant grade with the main valley; and the longer 
1 Jahresb. d. Geogr. Gesellsch. Munchen, 1886, pt. ii. See also Penck & 
Brickner, ‘ Die Alpen im Kiszeitalter’ Leipzig, 1901-02 ; A. Rothpletz, ‘ Hin 
eeologischer Querschnitt durch die Ost-Alpen ’ Munich, 1894 ; & A. P. Cole- 
man, Geol. Mag. 1902, p. 59. 
> Norges Geol. Underség. No. 28 (1900); & N. O. Holst, Sveriges Geol. 
Undersokn. ser. C, No. 180 (1899) p. 113. 
