Vol. 58. | HANGING VALLEYS IN THE ALPS AND HIMALAYAS, vals) 
originated since the lakes were in existence and, indeed, to be 
directly due to the presence of the waters of the lake. 
In these occurrences we have exactly what we might expect. 
A stream draining the hillside that borders a lake will, of necessity, 
eradually deepen its bed, and at the same time cut back its 
head-waters—in fact, establish its curve of erosion. The possible 
depth of this erosion will be limited by the level of the lake, below 
which no erosion can take place, but, on the contrary, deposition. 
While the lake remains at the same level, therefore, the stream is 
continually engaged in flattening the grade of its valley-floor, while 
below the level of the lake the old steeper grade is preserved. 
Should the level of the lake be lowered by erosion at its exit, the 
contrast of slope between the portions of the lateral valley formerly 
above and below the lake-surface respectively, will afford all the 
characters of a hanging valley. If this lowering of the lake be 
gradual, a gorge will be established cutting back into the lateral 
valley, for it must always be remembered that the adjustment of 
two discordant valleys can only take place from below, causing the 
incision to travel backwards at a steep, though diminishing angle. 
I would specially emphasize this law of readjustment, as it 
accounts for the effects of even a gradual lowering of the lake being 
visible for long afterwards in the tributary valleys, and also for 
long after the ice melted. Such a condition of things is well 
seen round the Italian lakes, especially the Lake of Como, as at 
Bellano, Menaggio, Varenna, and Argenio, and at Ostenno on the 
Lago di Lugano. The gorges already cut back by the readjustment 
are locally known as ‘oridos.’ Thus we have the Orido of Bellano, 
Orido of Ostenno, etc. In this case, then, it is not by the over- 
deepening of the main valley, that lateral hanging valleys and 
oridos are produced, but on account of its protection by the water 
of the lake. 
The remaining type, to which I should like to allude, is also pro- 
duced independently without any overdeepening of the main valley, 
and is only found in glaciated districts. These valleys are frequently 
connected with cirques, into which they merge at their upper end. 
They are produced in the first place by corrie-glaciers, which are 
gradually extended backward. A corrie-glacier of this character 
originates apparently in the following way :—The snow which falls 
in winter above the snow-line lodges more readily in the flatter por- 
tions of water-gullies formed in summer, and will tend to accumulate 
there, protecting the surface beneath from frost and water-action, 
while the rock-wall behind will continue to disintegrate, allowing 
more snow to accumulate each year, so that in time the flatter 
portion will extend backward into the hillside. In this way an 
upland glen filled with ice is gradually formed. I noticed many 
hanging glaciers of this description in Spitsbergen, and, though less 
common, they undoubtedly exist also in the Alps.’ 
? See Quart. Journ. Geol. Soc. vol. lv (1899) pl. xliv. 
