4 io 
THE TERTIARY VOLCANOES 
BOOK VIII 
The best locality for the examination of the junction of the main grano- 
phyre mass with the gabbros is inaccessible save by boat, and only in the 
calmest weather. It occurs in the great cliff on the northern side of the 
island between the north bay and the sea-stack known as the Bragstack. 
The line of contact emerges from below the sea-level, and ascends the cliff 
with a westward inclination of from 60° to 80°. Here, as in Skye, the acid 
rock underlies the basic masses, which are rudely bedded and much jointed. 
About 150 feet above the sea-level, the nearly vertical cliff breaks up into 
an exceedingly rocky and rugged acclivity, across which the junction seems 
to slope at a lower angle. But the place is hardly reachable, save perhaps 
by the intrepid, barefooted cragsmen of St. Kilda. 
Along the sharply defined line of contact the granophyre is close- 
grained, and sends a network of veins into the dark sheets of gabbro. The 
general features of the junction are represented in Fig. 362. The veins are 
Fig. 362.— Junction of granophyre anil gabbro, north side of St. Kilda. 
narrow, those nearest the main body of granophyre diverging from it at a 
still more acute angle than those from the mass of Meall Dearg (Fig. 376), 
and then branching so as to enclose masses of the gabbro and to run across 
them in long parallel veins. A characteristic feature of many of these veins, 
besides their narrowness, is their tendency to split up at the ends into mere 
fingers and threads as represented in Fig. 363. 
Owing to the depth of soil on the cultivated land, and of boulders and 
sand on the beach, the actual junction of the main body of granophyre with 
the gabbro is not seen on the southern shore. But a few yards to the 
from Trot. Judd, who there states that the rock supposed to be granite “ is seen under the micro- 
scope to he a quite different rock — a quartz-diorite. ” Some of the specimens from St. Kilda col- 
lected by Mr. Ross were exhibited at a meeting of the Geological Society on 25th January 1893. 
U itli regard to these Prof. Judd, in the course of the discussion on his paper on “Inclusions of 
Teitiaiy Granite in the Gabbro of the Cuillin Hills,” remarked : — “They show a dark rock tra- 
versed by veins of a light one, but the dark rock is not a gabbro and the light one is not a 
granite” {Quart. Joum. Gcol. Soc. vol. xlix. (1893), p. 198). 
