336 
THE TERTIARY VOLCANOES 
BOOK VIII 
out of account the invading granitoid rocks, and look upon the whole tract 
within which the gabbro occurs as originally one connected area, we find 
that it covered an elliptical space measuring about nine miles from south-west 
to north-east and six miles from north-west to south-east, and embracing 
at least 40 square miles. 1 But that its original size was greater is 
strikingly shown more particularly on the western margin, which like 
that of the basalt-escarpments, has obviously been determined by denuda- 
tion, for its separate beds present their truncated ends to the horizon all 
along the flanks of the Cuillins, from the head of Glen Brittle round to 
Loch Scavaig (Fig. 332), and from Strath na Creitheach round the 
southern flanks of Blath Bheinn to Loch Slapin and Strath More. 
The first point to be ascertained in regard to the gabbro and associated 
basic rocks of the mountainous tract is their connection in geological struc- 
ture and age with the bedded basalts of the plateau. This initial and 
fundamental relation, as Forbes long ago said, can be examined along the 
whole western and southern flank of the Cuillin Hills, from the foot of Glen 
Sligachan round to the mouth of Loch Scavaig. Even from a distance, the 
observer, who is favoured with clear weather, can readily trace the almost 
level sheets of basalt till they dip gently under the darker, more massive 
rock of the hills. Tourists, who approach Skye by way of Loch Coruisk, 
have an opportunity, as the steamer nears the island of Soay, of following 
with the eye the basalt-terraces of the promontory of Budh’ an Dunain 
until they disappear under the gabbro of the last spur of the .Cuillins that 
guards the western entrance to Loch Scavaig. 
What is so evident at a distance becomes still more striking when viewed 
from nearer ground. Nowhere can it be more impressively seen than at the 
head of Glen Brittle. Looking westwards, the traveller sees in front of him 
only the familiar level terraces and green slopes of the basalt-plateau, rising 
platform above platform to a height of nearly 1500 feet above the sea. But 
turning to the east, he beholds the dark, gloomy, cauldron-like Corry na 
Creiche, from which rise some of the ruggedest and loftiest crests of the 
Cuillins. On the hills that project from either side of this recess and half 
1 Though this and the other bosses are here spoken of as consisting of gabbro, it will be under- 
stood that this rock only constitutes the larger portion of their mass, which includes also 
dolerites and other more basic compounds, together with involved portions of the plateau- 
basalts and masses of agglomerate which probably mark the position of older vents. 
