DURING THE TERTIARY PERIOD IN THE BRITISH ISLES. 161 



Kilchrist. Several minor protrusions lie between that ridge and the flank of Beinn 

 Dearg. Another forms the moory ground above Corry ; several occur on the side of the 

 Sound of Scalpa, about Strollamus ; and one, already referred to, lies at the eastern base 

 of Blath Bheinn. 



In so extensive a tract, there is room for considerable diversity of composition and 

 texture among the rocks of which it consists. I have already stated that in some 

 places, more particularly in the central parts of the hills, the rock assumes the character of 

 a granite, being made up of a noncrystalline aggregate of quartz, orthoclase, plagioclase, 

 hornblende, and biotite, without granophyric structure. It is then a hornblende-biotite- 

 granite (quartz-syenite, granite-syenite of Zirkel, or amphibole-granitite of Eosenbusch). 

 By the development of the micropegmatitic structure and radiated spherical concretions, it 

 passes into granophyre. By the appearance of a felsitic ground-mass, it shades off into 

 different varieties of quartz-porphyry (rhyolite of some authors), sometimes with distinct 

 bi-pyramidal crystals of quartz.* As it is convenient to adopt some general term to 

 express the whole series of varieties in the Skye area, I shall use the word granophyre 

 for this purpose. 



That the large area of these rocks in Skye must have been the result of many 

 separate protrusions from distinct centres of emission may be inferred, I think, not 

 only from the varieties of petrographical character in the material, but also from the 

 peculiar topography of the ground, and perhaps from the curious relation which seems, 

 in some instances at least, to be traceable between the external features and apparent 

 internal structure of the hills. It will seen from the map (Plate II.) that in the area lying 

 to the east of Strath More, the granophyre is broken up into nearly detached portions by 

 intervening patches of older rocks. There can be little doubt that the mass of Beinn na 

 Caillich and the two Beinn Deargs is the product of a distinct orifice, if not of more 

 than one. Beinn na Cro, lying between its two deep bounding glens, is another 

 protrusion. The western cones stand so closely together that their screes meet at the 

 bottoms of the intervening valleys. Yet each group is not improbably the result of 

 emission from an independent funnel. 



But, though I believe this large area of granitoid rock to have proceeded not from one 

 but from many orifices, I have only here and there obtained, from the individual hills 

 themselves, indications of an internal structure suggestive of distinct and successive 

 protrusions of material from the same vent of discharge. On the outer declivities of 

 some of the cones, we may detect a repetition of that rudely bedded structure to which 

 reference has been made as occurring in Eum. This structure is specially observable 

 along the east side of Glen Sligachan. Down the northern slopes of Marsco the 

 granophyre (here in part a hornblende-biotite-granite) is disposed in massive sheets 

 or beds that plunge outwards from the centre of the hill at angles of 30° to 40°. On the 

 southern front of the same graceful cone, as well as on the flanks of its neighbour, Ruadh 



* The best account yet published of these varieties in Skye is that by Prof. Zirkel, Zeitsch. Deutsch. Geol. Gesellsch., 

 xxiii. (1871) p. 88. 



