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Messrs. Hicks §& Davies—Pre-Cambrian Rocks of Ross-shire. 103 
II].—On toe Pre-CamBrian Rocks or West AND CENTRAL 
Ross-SHIRE. 
By Henry Hicks, M.D., F.G.S. 
WitH PETROLOGICAL NOTES. 
By T. Davies, F.G.S., of the British Museum. 
(PLATE IV.) 
PORTION of the district referred to in this paper was described 
by me in a communication to the Geological Society, on May 
22nd, 1878, and this was afterwards published in the Quart. Journ. 
Geol. Soc. vol. xxxiv. In that paper, however, many of the facts 
which had led me to the conclusions stated therein had to be 
omitted, and the important evidence derived from the microscopical 
examination of the rocks was hardly touched upon. It was then 
intended that this evidence should be given in an appendix to 
the paper, but, unfortunately, circumstances at the time prevented it. 
As, since then, doubts have been expressed as to some of the 
interpretations given, it is not altogether, perhaps, to be regretted 
that this delay has occurred; especially as it has enabled a larger 
series of petrological observations and comparisons to be made. 
In entering at first upon this inquiry, my main object was to 
endeavour to realize, by geological and petrological observations, 
the relationship to be made out between the gneiss rocks of the 
North Western Highlands, and the Pre-Cambrian rocks of Wales, 
upon which I have been working for so many years. Other 
questions, however, arose in the course of the inquiry, and some 
conclusions were arrived at, which have necessitated a more detailed 
arrangement. 
In the petrological descriptions (as on many previous occasions) I 
am greatly indebted to the experienced aid so readily given by Mr. 
T. Davies, F.G.S., of the British Museum. His long acquaintance 
with the minerals and microscopical characters of the older or Pre- 
Cambrian rocks, from various countries, and well-known labours in 
petrology generally, render his notes specially valuable in this 
inquiry. 
Gaerloch, Poolewe, and Loch Torridon. 
In the area to be described (see map) the most westerly exposures 
of the Pre-Cambrian rocks are to be found at and about Gaerloch. 
To the N. and E. of this place, over a considerable district, they are 
uncovered by newer formations, but westward along both sides of 
the loch, Cambrian sandstones and conglomerates lie at low angles 
on the up-turned edges of these older rocks. In so extensive an 
area, as would naturally be expected, considerable differences occur 
in the composition of the rocks at various points, and those varieties 
which appear most characteristic of the group in one place, may be 
entirely absent at another. Hitherto no detailed observations seem 
to have been made on these rocks in this area, but a few special 
varieties have been noted by Macculloch, Nicol, and Murchison in 
their papers. They have been generally designated ‘fundamental 
gneiss,” and associated with the western gneiss of Sutherland, and 
