nt phenomena are centred; for here we meet with
representatives of the acid (or highly silicated) group of rocks, and
of remarkable beds of gabbro, which have long attracted the attention of
petrologists. These latter beds, throughout a considerable distance
round the flanks of the Cuillin Hills, are interposed between the acid
rocks and the plateau-basalts; but towards the north, on approaching
Lough Sligahan, the acid rocks, consisting of granophyres,
quartz-porphyries, and hornblendic-granitites, are in direct contact
with the plateau-basalts; and, according to the very circumstantial
account of Sir A. Geikie, are intrusive into them; not only sending
veins into the basaltic sheets, but also producing a marked alteration
in their structure where they approach the newer intrusive mass. Equally
circumstantial is the same author's account of the relations of the
granophyres to the gabbros,[1] as seen at Meall Dearg and the western
border of the Cuillin Hills--where the former rock may be seen to send
numerous veins into the latter. Not only is this so, but the granophyre
is frequently seen to truncate, and abruptly terminate some of the
basaltic dykes by which the basic sheets are traversed--as in the
neighbourhood of Beinn na Dubhaic. All these phenomena strongly remind
us of the conditions of similar rocks amongst the mountains of Mourne
and Carlingford in Ireland; where, at Barnaveve, the syenite (or
hornblendic quartz-felsite) is seen to break through the masses of
olivine gabbro, and send numerous veins into this latter rock.[2]

The interpretation here briefly sketched differs widely from that
arrived at by Professor Judd. The granitoid masses of the Red Mountains
(Beinn Dearg) and the neighbouring heights are, in his view, the roots
of the great volcano from which were erupted the various lavas; the
earlier eruptions producing the acid lavas, to be followed by the
gabbros, and these by the plateau-basaltic sheets, which stretch away
towards the north and west into several peninsulas. Thus he holds that
"the rocks of basic composition were ejected subsequently to those of
the acid variety," and appeals to various sections in confirmation of
this view.[3] To reconcile these views is at present impossible; but as
the controversy between these two observers is probably not yet closed,
there is room for hope that the true interpretation of the relations of
these rocks to each other will ere long be fully established.