CHAP. XLVI 
THE ACID BOSSES OF SKYE 
379 
little change. The most marked examples of this metamorphism are those 
in which the Cambrian limestone of Skye has been converted into a pure 
white saccharoid marble. But the most interesting to the student of volcanic 
action are those where the altered rocks are older parts of the volcanic series. 
As the bosses of each volcanic area offer distinctive peculiarities they will 
here be described geographically. 
i. THE ACID BOSSES OF SKYE 
It is in the island of Skye that the granophyre and granite bosses attain 
their largest dimensions and afford, on the whole, the most complete evidence 
of their structures and their relations to the other parts of the volcanic series 
(Map VI.). They cover there a total area of about 25 square miles, and form 
characteristic groups of hills from 2000 to 2500 feet in height. On the 
south-east side, three conspicuous cones (the Bed Hills) rise from the valley of 
Strath (Beinn Dearg Mhor, Beinn Dearg Bheag and Beinn na Caillich). 
A solitary graceful pointed cone (Beinn na (Jro) stands between Strathmore 
and Strathbeg, while to the north-west a continuous chain of connected 
cones runs from Loch Sligachan up into the heart of the Cuillin Hills. 
Their conical outlines, their smooth declivities, marked with long diverging 
lines of screes, and their pale reddish or reddish-yellow line, that deepens 
after a shower into glowing orange, mark off these hills from all the sur- 
rounding eminences, and form in especial a singular contrast to the black, 
spiry, and rugged contours of the gabbro heights to the west of them. 
Besides this large continuous mass, a number of minor bosses are scattered 
over the district. Of these the largest forms the ridge of Beinn an Dub- 
haich, south of Loch Kilchrist. Several minor protrusions lie between that 
ridge and the flank of Beinn Dearg. Others protrude through 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 the neighbouring island of Ilaasay, a large area of granophyre 
likewise occurs, which will be described with the Sills in later pages. 
In so extensive a district there is room for considerable diversity of 
composition and texture among the rocks. As already stated, in some places, 
more particularly hi the central parts of the hills, the acid material 
assumes the character of a granite, being made up of a holoerystalline aggre- 
gate ot quartz, orthoclase, plagioclase, hornblende and biotite, without grano- 
phyric structure, and thus becomes a liornblende-biotite-granite (quartz- 
syenite, granite-syenite of Zirkel, or amphibole-granitite of Eosenbuscli). By 
the development of the micropegmatitic structure and radiated spherical con- 
cretions, it passes into granophyre. By the appearance of a felsitic ground- 
mass, it shades off into different varieties of quartz-porphyry or rhyolite, 
sometimes with distinct hi- pyramidal crystals of quartz. 1 This change, 
which here and there is observable along the edge of a boss, is sometimes 
accompanied with an ample development of spherulitic and flow-structures. 
1 The best account yet published of these varieties in Skye is that by Prof. Zirkel Zcitsch. 
Deutsch. Geol. Gesellsch. xxiii. (1871) p. 88. 
