1 82 The Scottish Naturalist. 



include the Tarff, its chief tributary, which joins it not far from 

 Loch Tilt, we must add another lo miles. The scenery of the 

 Tarff is quite different from that of the Tilt, being, except at its 

 lowest part, desolate and dreary in the extreme. Where it joins 

 the Tilt its course is a series of alternate cascades and pools, but 

 further up it winds through flat moors encircled by rounded 

 mountain-masses. 



A little higher up than Pool Tarff (the junction of the Tilt and 

 Tarff) the Tilt has another large influent in the Lochain, which 

 flows from Loch Loch on the south of Ben-a-Ghlo. Further 

 down the glen it has many tributaries, but mostly of small size, 

 with the exception of three or four, which, with their glens, join 

 Glen Tilt on its northern side. 



In altitude above sea-level. Glen Tilt itself varies from 400 to 

 2000 feet, the surrounding mountains attaining frequently a 

 height of 3000, and in some cases of nearly 3700 feet. Imme- 

 diately to the north of Glen Tilt lies the Forest of Athole ; while 

 the south side of the glen, though frequently invaded by the red 

 deer, affords grazing to many sheep. Mucli has been said and 

 written for and against deer-forests; but as a zoologist and 

 botanist — and it is in that capacity only that the subject can be 

 considered in these pages — I am strongly of opinion that deer- 

 forests have been very beneficial in preserving both animals and 

 plants which would long ago have vanished had the ground been 

 closely grazed by sheep. Glen Tilt affords a good example of this. 

 The northern, or forest side, is most richly clothed with a luxu- 

 riant carpet of wild flowers, and teems with insect life ; on the 

 other hand, the south, or sheep-grazed side, is covered with 

 scarcely any plants but grass and fern, save where steep rocks 

 offer a resting-place beyond the reach of the sheep ; and in har- 

 mony with this lack of variety in the vegetation, scarcely an insect 

 is. to be seen. Glen Bruar, which runs parallel to Glen Tilt, and 

 is grazed by sheep, presents a similar case. No doubt there are 

 other causes at work, but I believe it is chiefly owing to its being 

 deer-forest that one side of Glen Tilt is so much richer than the 

 other. 



Geologically Glen Tilt is very interesting ground, but it would 

 require a great deal more space than we can aftbrd even to treat 

 very cursorily of its features. For the purposes of this paper it 

 will be enough to say that the formation is the Lower Silurian, 

 and that the rocks are chiefly of a gneissose or quartzose char- 

 acter, and of a kind that do not wcatiicr much, and therefore are 



