323 
THE TERTIARY VOLCANOES 
BOOK VIII 
summit of Ben Hiant and strike into the Jurassic outlier below, intensely 
indurated shale may be seen lying between two of the dolerites, which are 
unquestionably sills that have been injected into the Jurassic series. 
The ridge of Ben Hiant is thus found to consist of a thick and com- 
plex series of sills, some of which are not traceable beyond the side of the 
mountain, while others can be followed outwards among the surrounding 
rocks. The specially marked dyke-like sills diverge from the main mass 
and run for some distance north-eastward, one of them, fully a mile long. 
a 
Fig. 327. — Section of two Sills in schistose grits, west end of Beinn na h-Urchracli, Ardnanmrclian. 
a a., crystalline schists ; h, neck of volcanic agglomerate ; c, small sill ; D, massive sill of Beinn 11a h-Urchraclf; 
F, sill proceeding from the series forming Ben Hiant and joining that of Beinn na h-Urchrach. 
descending among the schists into the valley and ascending into the basalt- 
plateau on the opposite side . 1 
On the south-east side of the mountain where the bedded basalts can 
be traced close up to the intrusive dolerites, they are found to present the 
usual dull indurated aspect so characteristic of contact alteration among 
these rocks. There cannot therefore be any doubt that Ben Hiant never 
was itself a volcano. Its rocks are characteristically those of subterranean 
intrusions. They seem to have been injected from a line of fissure or from 
several such lines, running in a general north-easterly direction, at some 
late part of the volcanic period. The group of agglomerate necks of older 
date shows that already the ground underneath had been drilled by a 
number of distinct volcanic funnels, and discloses a weak part in the 
terrestrial crust. 
iv. FAKOE ISLES 
In the Faroe Islands the actual base of the volcanic series is nowhere 
visible. Hence, the great lower platform of intrusive sheets being there 
concealed, this feature of the basalt-plateaux is less conspicuous than it is 
in the Inner Hebrides. A number of sills, however, have been noticed by 
previous observers , 2 and I have observed others on the sides of Stromci, 
Kalso, Ivuno and other islands. In the lofty precipices of the Haralds- 
fjord, many of the massive light-coloured prismatic sheets are intrusive, for 
though they preserve their parallelism with the bedded sheets for consider- 
1 The sills of Ben Hiant descend on the south-west side into the sea, and can he examined 
along the slopes and the beach, where Professor Judd has mapped a continuous platform of 
agglomerate. The hroad hollow between that mountain and Beinn na h-Urchracli, over which 
he has spread his “augite -andesite lavas,” appears to he underlain mainly by the crystalline 
schists through which sills from Ben Hiant have been injected. The northern eminence, which 
he lias united with Ben Hiant, is entirely separate and, as above shown, is an obvious sill. 
2 See in particular Prof. James Geikie and Mr. Lomas, in the papers already cited on p. 191- 
