536 Rev. T. O. Bonney — Cirque in the Hills of Sky e. 



Before proceeding to discuss the formation of this Cirque in Skye, 

 a few words about the geology of the island may not be out of place. 

 Five very distinct regions are at once evident, even to the passing 

 traveller. To the south is a long rolling line of uplands — quartzites, 

 gneiss, and schists — resembling in their general contour the great 

 mainland mass of altered Cambrian and Silurian rocks, of which 

 they are only a prolongation. To this succeeds a wide open valley 

 or plain, the Strath, occupied by sedimentary rocks of Mesozoic age, 

 Lias, and Inferior Oolite, which, though occasionally shattered, 

 pierced, and overflowed by igneous rocks, rarely rises to any great 

 height above the sea. 



Another mountain district now succeeds, itself comprising two 

 very distinct regions. To the west, rising some 3000 feet, are the 

 Cuchullin hills — wild aiguilles, whose crags of sombre hypersthene 

 rock offer the grandest scenery in Scotland ; to the east, and lower 

 by full 1000 feet, is an irregular mass of hills of a peculiar rounded 

 contour, the Syenite region. To the north of this comes the unevenly 

 outlined trap district, forming the larger half of the island, where 

 huge sheets of basalt break through and overlie rocks of Oolitic age, 

 and rise occasionally in great plateaux to a height of full 1500 feet 

 above the sea. 



The syenite of which I speak has burst through the Jurassic 

 rocks of the Strath, occasionally greatly displacing and altering 

 them. In colour it is reddish-grey, giving the hills in the distance 

 a tint varying from a rusty hue to one that in some lights is almost 

 white. It appears to consist chiefly of orthoclase-feldspar, and 

 hornblende, but weathers so easily that it is very difficult to obtain 

 a specimen unaffected by decomposition ; notwithstanding this, as is 

 the case with other hornblendic rocks, it is very tough and difficult 

 to break,^ 



The date of this syenite mass is as yet uncertain. Without doubt 

 it is posterior to all the Jurassic rocks of the island, and Professor 

 Geikie ^ is of opinion that it, like the igneous rocks of the northern 

 plateaux, is of Miocene age. Neither is it easy to say how far its 

 present peculiar outline is the result of denudation. Without doubt 

 its summits have been lowered by the almost incessant showers that 

 have for thousands of years been driven against them by the Atlantic 

 breezes ; and the valleys among them have, to a great extent, been 

 excavated by the same agencies, but still their peculiar forms, 

 reminding us of the Puy de Dome, Sarcoui, and other domite 

 hills in Auvergne, suggest that their present may, to a considerable 

 extent, resemble their original configuration, and that these great 

 bosses may have been excreted in a pasty state from numerous 

 subjacent vents. 



To proceed, however, with the special subject of this paper. On 

 landing at Broadford, a little village at the north-east angle of the 

 Strath, I was at once struck with two conspicuous corries, one on 

 the side of Ben na Caillich, a fine dome-shaped mass of this syenite ; 



1 MacCuUoch (Western Isles, vol. i., p. 267) notices this tendency to decompose. 

 "^ Quart. Journ. Geol, Soc, vol. xxvii., 282. 



