CXIii PROCEEDINGS—PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
protected by a covering of soil or vegetation, this work of frost goes 
on all winter, not only on the outer surface, but in all the joints and 
fissures of the rock, so that not only is the face crumbled into 
powder, but great blocks, perhaps tons in weight, are hurled to the 
foot of the slope. You must all have observed the results of this 
action in some of our rocky Highland glens, such as Glen Ogle, 
Glen Lyon, etc. The same thing may be seen on a very much 
grander scale in some of the Norwegian valleys, such as the Naerodal 
and the Norangsdal, where I have travelled for miles through the 
most stupendous rock ruins. 
To return again for a moment to our Barracks-wall illustration,— 
if nature had been left to her own courses (instead of being inter¬ 
fered with by the scavenger), the snow would have melted and 
deposited the sand on the footpath; from thence the first shower of 
rain would have washed it into the gutter, and finally into the- river. 
Precisely the same process goes on on the hillside. The loosened 
particles lie at the foot of the rocks and crags till the rain carries 
them into the nearest runnel, thence they reach the stream, and at 
last the river. 
Last summer I had an example of what a mountain rain-storm 
can do, which enabled me to realise the denuding power of running 
water more clearly than I had done before. It was early evening, 
and I was returning by train from Dalmally to Perth. All morning 
it had rained heavily, and the mountains had been obscured by thick 
mist; but by the time I started the rain had ceased and the mists be¬ 
gan to roll up the mountain sides, revealing a scene both most im¬ 
pressive in its grandeur of outline and its beauty of colouring, and 
also most instructive in its geological teaching. The sides of Ben 
Cruachan were seamed with a close net-work of mountain torrents 
gleaming white in the evening sunlight, and producing in the distance 
a dull continuous roar, as a thousand miniature cascades leaped down 
the rocks. The sound is exquisitely described by Wordsworth, who 
must often have listened to the same music amid his own lakeland 
hills. The following stanza occurs in “Lines composed at Grasmere, 
during a walk, one evening, after a stormy day ” :— 
“ Loud is the vale !—the voice is up 
With which she speaks when storms are gone, 
A mighty unison of streams ! 
Of all her voices, one ! ” 
All through Glen Lochy, Strath Fillan, and the long Glen Dochart, 
the hill sides presented the same appearance. The sudden heavy 
rainfall had revealed an infinite number of water-courses, whose 
existence was not suspected until pencilled by the foaming waters. 
Here, then, was one of Nature’s carving tools at work in earnest, 
namely, running water. That it was doing real destructive work was 
evidenced by the colour of the water in the larger streams, dark brown 
with peat, sand, clay, and other detritus. 
Time will not allow me to follow the course and the work of the 
