432 
THE TERTIARY VOLCANOES 
BOOK VIII 
times distinctly spherulitic (west side of Cam Nathragh, next Lias shale). 
Under the microscope the rock is seen to he a fine-grained granophyrie 
porphyry or porphyritie granophyre. It caps Carn Dearg (636 feet) above 
Suisnish, where it covers a space of nearly a square mile, and reaches at its 
eastern extremity (Beiim Bliuidhe), a height of 908 feet above the sea (Fig. 
249). This rock rests upon a sill of dolerite, and is apparently split up by 
it. But, as I have already stated, the basic rock is probably the older of 
the two, and the granophyre seems to have wedged itself between two earlier 
doleritic sheets. To the north-west of Carn Dearg, above the northern end 
of the crofts of Suisnish, the same sill, or one occupying a similar position, 
crops out between masses of granophyre, and is intersected by narrow veins 
from that rock. 
Though severed by denudation, the large sheets of granophyre to the 
east of Beinn Bhuidhe are no doubt continuations of the Carn Dearg mass, 
or at least occupy a similar position. That they are completely unconform- 
able to the Jurassic strata is shown by the fact, that while at Suisnish they 
lie on sandstones which must be fully 1000 feet above the bottom of the 
Lias, only two miles to the east they are found resting on the very basement 
limestones, within a few yards from the underlying quartzite and Torridon 
sandstone. I do not think that this transgression can he accounted for by 
intrusion obliquely across the stratification. 1 regard it as arising from the 
eruptive rock having forced its way between the bottom of the now 
vanished basalt-plateau and the denuded surface of Jurassic rocks, over which 
the basalts were poured. The platform underneath these granophyre sills 
thus represents, in my opinion, the terrestrial surface before the beginning 
of the volcanic period. 
But there is abundant proof that though the intruded granophyre sills 
followed generally this plane of separation, they did not rigidly adher to it, 
but burrowed, as it were, along lower horizons. Thus on the south-east 
front of Beinn a’ Chaim, which forms so fine an escarpment above the valley 
of Heast, the base of the granophyre, after creeping upward across successive 
beds of limestone, sends out a narrow tongue into these strata, and continues 
its course a little higher up in the Lias. The same rock, after spreading out 
into the broad flat table-land of Beinn a’ Chairn (983 feet), rapidly con- 
tracts north-eastwards into a narrow strip which forms the crest of the 
ridge, and at once suggests a much-weathered lava-stream. The resemblance 
to a couUe is heightened by the curious thinning off of the rocks where the two 
streams emerge from the Heast lochs ; it looks as if the igneous mass were 
a mere superficial ridge which had been cut down by erosion, so as to 
expose the shales beneath it. But that the granophyre is really a sill becomes 
abundantly clear at its eastern end, where we find that it consists of two 
separate sheets with intervening Liassic shales. The structure of this 
interesting locality is shown in Fig. 372. In this instance also, there is 
evidence that the acid sills are younger than the basic, for the upper sheet 
of granophyre sends up into the overlying dark basaltic rock narrow vertical 
felsitic veins, a quarter of an inch to an inch in width, which being more 
