340 
THE TERTIARY VOLCANOES 
BOOK VIII 
these rocks have reached the valley, they have already lost their usual 
brown colour and crumbling surfaces, and have assumed the indurated 
splintery character, though still showing their amygdaloidal structure. They 
are much traversed by felsitic veins and strings which proceed from a 
broad band of fine-grained hornblende-granite that runs up the bottom of the 
Coire Uaigneicli and, ascending the col, crosses it south-westwards into the 
G-len nan Leac. On the left or south-eastern side of this intrusive mass, a 
portion of Lias shales and limestone (here and there altered into white 
marble) is traceable for several hundred yards up the stream. 1 
The bedded basalts of Strathaird, after dipping down towards the N.X.W., 
bend up where they are interbanded with dolerites and gabbros, and form 
the prominence called An Stac, which rises as the eastern boundary of the 
Coire Uaigneicli. Their steep dip away from the mountain is well seen 
from the east side, and their outward inclination is continued into the ridge 
to the southward. Similar rocks appear on the other flank of the band of 
granite, and form the base of Blath Bheinn. They are likewise continued 
in the mountains further north called Sgurr nan Each and Belig, where 
they dip in a northerly direction away from Blath Bheinn, which seems 
to be the centre of uprise, with the gabbro-sheets dipping away from 
it. The bedded basalts have been traced by Mr. Harker up to a height of 
well over 2000 feet on the Blath Bheinn range. They are of the usual 
altered, indurated, and splintery character. The intrusive sheets interposed 
between them become thicker and more abundant higher up, until they 
constitute the main mass of the mountain. But that they are in separate 
sheets, and not in one amorphous mass, can be recognized by the parallel 
lines that mark their boundaries. The junction of the gabbro sills and 
the lavas is a very irregular one, portions of the latter rocks being enveloped 
in the intrusive sills. 
The granite which sends out veins into the surrounding rocks is 
obviously the youngest protrusion of the locality, except of course the 
basalt-dykes which cross it, and which are nowhere seen in a more imposing 
display than round the flanks of Blath Bheinn. A section across the corry 
shows the structure represented in Fig. 334. 
It is thus demonstrable that when its line of junction with the sur- 
rounding plateau-basalts is traced in some detail, the gabbro is found to 
overlie them as a whole, but also to be intercalated with them in innumer- 
able beds, bands, or veins which rapidly die out as they recede outwards 
from the main central mass ; that these interposed beds are intrusive sheets 
or sills from that mass which have cut off and enveloped portions of the 
basalts, and that the contiguous bedded basalts show more or less marked 
metamorphism. 
We have now to consider the structure of the interior of the gabbro 
1 This limestone was formerly identified by me with the Cambrian strata of the district. It 
was noticed by Von Oyenhausen and Von Dechen, who, as Mr. Harker has recently ascertained, 
correctly believed it to be a portion of the Lias torn off and carried upward by the eruptive 
rocks (Karsten’s Archiv, i. p. 79). 
