eet ae 
Pre-Cambrian Rocks of Ross-shire. 107 
of a larger quartz crystal, the whole of the gneiss-like aspect of 
this rock is due. The felspar is principally orthoclase, much altered, 
and with a little plagioclase is occasionally developed into larger 
crystals. Mica is very sparse, scattered irregularly through the 
mass, though a very few attenuated waves of folia are present, con- 
sisting principally of muscovite. Limonite as pseudomorphs after 
minute cubic crystals of iron pyrites is frequent throughout.—T.D. ] 
I was unable to examine the district further north towards Poolewe, 
but Prof. Seeley, who had gone over this ground some time previously, 
has kindly allowed me to examine a collection made by him in that 
direction. In speaking of the rocks generally, he says that he found 
a great variability amongst them. This agrees with what I noticed 
also in travelling further east on a parallel line, and probably across 
the same beds. Amongst Prof. Seeley’s specimens may be men- 
tioned chiefly some highly quartzose gneisses, an augen-gneiss, a 
large-grained very dense hornblende rock, and a hornblende gneiss, 
all as nearly as possible identical with specimens I collected in 1878 
at Ben Fyn (in the so-called eastern gneiss). Other rocks which 
may be considered perhaps by some more typical even than these 
of the western gneiss occur here also, such as a reddish felspathic 
rock with strings of epidote permeating it, and a large-grained 
granitoid gneiss, Note No. 3. A band of limestone also has been 
mentioned by Murchison running parallel to the gneisses to the S.E. 
of Poolewe. 
[ Nore 8.—A medium-grained crystalline rock consisting of quartz, 
orthoclase. and some plagioclase with mica. The latter constituent, 
in addition to its irregular distribution throughout the rock, forms 
also thin bands which are more or less parallel, and to which its 
gneissic aspect appears to be entirely due. Seen in thin section the 
intimate crystalline structure of the constituents greatly resembles 
that of atypical granite, where the minerals are developed without 
any tendency to parallelism ; the evidences of a foliation here being 
entirely absent except in the wavy bands of mica. The quartz which 
constitutes the larger part appears to be remarkably free from fluid 
inclusions, though traversed by numerous bands of exceedingly 
minute grains, which under a {-inch objective are resolved into 
minute spherical and oval cavities which appear to be empty, as 
I failed to recognize in any of them the usual indications of fluid 
contents. Orthoclase is the predominant felspar, and as well as 
being in a partly altered condition, is more or less obscure, 
owing to the presence of abundance of similar minute empty cavities 
as occur in the quartz. Similar inclusions, though mostly containing 
fluid, were recognized by Zirkel' in the orthoclase of the gneisses of 
the Clover Cation, Humboldt Mountains, Nevada. Both the felspars 
frequently inclose individual crystalline grains of quartz, which from 
their rounded contours recall to mind the quartz of many quartz- 
felsites. Plagioclase is much less frequent, is in fresher condition 
and nearly free from inclusions. Mica is dark greenish-brown, 
strongly dichroic, and is probably biotite. Sphene with a little 
. } Microscopical Petrography, by Ferdinand Zirkel, Washington, 1876, p. 17. 
