548 Proceedings of the Royal Society 
smoothly covered with fine heather, the favourite breeding-place 
for grouse, and tolerably dry, except where small patches of peaty 
bog show themselves here and there. This structure is often well 
exemplified among the mountains of Grlen-Shee. Again, when the 
spurs of a mountain are ridgy, the ridges are sometimes separated 
from one another by an upland valley, often very grassy, especially 
towards its head or “ corrie,” but likewise apt in many places to be 
boggy, and there abounding in peat, and in denuding cuts which 
expose the peat to atmospheric influences. Grood examples of such 
upland valleys are to be seen on the Cobbler, and on its higher 
northern neighbour Ben-Arnen, where they face Arrochar eastward, 
and also on Ben-Lomond northward from its peak. Exposed peat 
constitutes on the whole no great proportion of the surface of most 
mountains in the Highlands. 
It follows from this structure, that in most districts of the High- 
lands rain and melted snow find little to dissolve in descending the 
mountain sides ; and their steepness causes the streams to tarry a 
very short time in their descent, and to drain off quickly the excess 
of water in flood-time. All these circumstances combine to render 
the streams and lakes of the Highlands uncommonly pure in dry 
weather, and not materially less so even in heavy floods. Among 
the granite ranges, such as in the G-oat-Fell district of Arran, the 
streams, such as the Rosa and Sannox, are beautifully clear 
and colourless in the highest floods. The temporary water-falls 
which then streak the mountain slopes, present to the eye the 
purest whiteness; and on filling a glass tumbler from a stream, the 
water, after the instant subsidence of a few coarse particles of granite 
sand, is seen to be perfectly transparent and free from colour. In 
the mica-slate districts of the near G-rampians the streams are 
equally pure in dry weather. But after rains they are visibly 
brownish, yet so slightly that in a common water-bottle on a dinner- 
table the colour may readily escape notice. 
During last autumn I had frequent opportunities of examining, 
in various circumstances, the water of one of these mica-slate 
streamlets, which is used for supplying a villa near Loch-Gfoil-head. 
The stream descends the steep eastern slope of <£ The Cruach,” a 
hill which land-locks the upper part of Loch Gfoil on its west shore 
at a point about a mile and a half from the Head. Although only 
