950 DR ROBERT CAMPBELL ON 
however, suggests that the centres of eruption were situated along two lines, one of 
which lay north of the Highland fault, while the other is concealed under the North 
Sea. The former we shall call the ‘“ Highland group of volcanoes”: the latter includes 
at least two eruptive foci—one in the vicinity of Montrose, the other off the coast at 
Crawton—and these we shall designate the ‘‘ Montrose centre” and the ‘Crawton 
centre” respectively. 
(a) The Highland Group of Voleanoes.—The lavas which emanated from these 
volcanoes include the dacites and andesites which extend from Temple of Fiddes to the 
Highland fault near Bogincabers. Two or three basic flows associated with them 
perhaps belong rather to the Crawton basalt group; but since in the district where the 
two groups approach one another the nature of the solid geology is obscured by the 
great development of drift, it is difficult to obtain satisfactory field evidence. ‘The fact 
that boulders of the basic lavas are absent from the associated conglomerates rather 
favours the supposition that the basalts came from the east or south-east. The acid 
andesites never appear in the coast section, and they attain their maximum develop- 
ment in close proximity to the Highland fault. It is not from the lavas, however, that 
we get the most convincing evidence as to the nature of the eruptions from this High- 
land centre or centres. One of the most remarkable features in the succession, from 
the base of the Downtonian to the top of the Arbuthnott group, is the great part played 
by acid tuffs and volcanic conglomerates. Wherever continuous belts of these can be 
traced inland they are found to thicken in the direction of the Highland fault. The 
constant association of their predominating rhyolite and acid andesite boulders with 
boulders of ‘‘ Highland” rocks indicates that the material has come from the north or 
north-west. The extraordinary thickness of the successive voleanic conglomerates 
implies the removal of a vast accumulation of acid lavas from the Highland area. 
Throughout the whole of the Downtonian and a considerable part of Lower Old Red 
Sandstone times there must have flourished, along the tract now occupied by granites 
and schists, a series of volcanoes whose chief products were rhyolite and acid andesite 
lavas and rhyolitic and andesitic tuffs. No vents, so far as I know, have been detected 
in that region; but some of the intrusive masses of quartz porphyry may possibly 
represent the position of centres of eruption. It is tolerably certain that there is a 
genetic connection between the quartz porphyries and some of the newer granites of 
the Eastern Grampians and the igneous rocks of Downtonian and Lower Old Red 
Sandstone age of south-eastern Kincardineshire. 
(b) The Crawton Centre.—The lavas erupted from this centre include the doleritic 
basalts of Tremuda Bay and the porphyritic basalts of the Crawton type. These lava 
groups thin off to north, south, and west from Tremuda Bay and Crawton, so that the 
volcanoes from which they came must have been somewhere to the east of the present 
coast line. I can find no evidence of tuffs belonging to this series. ‘The acid tufts and 
volcanic conglomerates, which underlie the Crawton basalts at Kinneff, have come from 
a centre somewhere to the north-west, and probably belong to the Highland group of 
