698 PROF. T. G. BONNEY ON [ Nov. 1902, 
above the sea. The ascent to these is commonly a rocky wall, some 
800 feet high, but the slope of the névé below is generally not rapid 
and that of the ice-stream almost gentle ; for a considerable length 
of the glacier lies between rather over 8000 feet and rather under 
7000 feet above sea-level. From its foot (about 6200 feet) the 
valley retains its dominant features for perhaps 24 miles, except 
that it tends to become narrower, its bed being rather flat and stony. 
Near the Grimsel Hospiz (6160 feet), famous for the surrounding 
roches moutonnées, the Aar turns sharply from north-east to 
north-north-west, and begins a rapid descent for about 1500 feet 
through the Upper Haslithal. In section, this part of the valley is 
a regular V, cut completely in crystalline rocks, which, as is well- 
known, are wonderfully ice-worn, and the marks of the glacier may 
be traced in places to within 2 or 3 yards of the torrent. A rise in 
temperature of 10° would probably efface the Unter-Aar Glacier, 
and give us in its place a rather trench-like valley, at the head of 
which the rock-wall of the Strahleck would rise from a snow- 
bed of very moderate size. If, then, this upper trench, now mostly 
occupied by glacier, be the work of the ice, so must be the lower part 
below the Grimsel. Yet that is a regular V: its buttresses, though 
wonderfully moulded by ice-action, still retain the ridges character- 
istic of sculpture by ordinary meteoric forces, and shallow glens 
may be occasionally seen on either side, descending from the moun- 
tain-crests. Though the ice has nowhere left its mark on the 
Alps more conspicuously than here, it has not been able to obliterate 
the leading lines of a waterworn valley. 
It would be easy to multiply instances from other parts of the 
Alps. These exhibit varietal differences, according to the nature of 
the rocks ; and the physical features of the limestone-districts differ 
in some respects from those of the crystalline. But, speaking of the 
latter only (in order to avoid too much complexity), I may say that 
all the valleys, small and large, in the lower as well as the higher 
districts, are shaped on the same general pattern, the superimposed 
effects of ice becoming more conspicuous as we get farther from the 
sea-level, and nearer to their heads. ‘The evidence, so far as I can 
read it, indicates that the isolation of a tributary from the principal 
valley—in other words, the conversion of the former into a ‘hanging 
valley,’ depends upon whether the latter could become the path of 
a powerful, and especially of a glacier-fed torrent—-that is, it is 
very much a question of the forces and of the environments. In 
the Cottian Alps, from which glaciers have practically disappeared 
and where the streams are generally clear, rock-gorges, so far as I 
remember, are not as a rule conspicuous. But in Dauphiné, in all 
the great mountain-mass connecting its central peaks with the 
Aiguilles of Mont Blanc, throughout the valleys and passes of 
Switzerland, and in the Tyrol (of all which I can speak from 
personal knowledge), I have observed only varietal distinctions, 
together with many common features which appear to me inexplicable 
on any hypothesis of ice-excavation ; and have not found one which 
