Pre-Cambrian Rocks of Ross-shire. 269 
In walking over these mountains in all directions, I did not find a 
single spot where the rocks were not completely crystalline, and the 
vertical thickness traversed over must have been very great. There 
was no evidence of aselective metamorphism, but all were equally 
affected. The mica schists, the true gneisses, and the hornblende 
rocks, all equally proved that we had here no partial change due to 
some local cause, but a universal state of crystallization, such as could 
only have been induced by a wide-spreading cause. 
Looking at the physical as well as the petrological evidence 
furnished by these mountains, I have no hesitation whatever in 
claiming for the rocks composing them a Pre-Cambrian age, and I 
believe, moreover, that they can be correlated in almost every par- 
ticular with the so-called fundamental rocks along the west coast, 
especially with those exposed about Gaerloch. The petrological 
notes by Mr. Davies will enable all to realize the present condition of 
the chief varieties in each area, and if a comparison is made, it will 
be at once apparent that whatever their primary condition may have 
been, the rocks in these central mountains have undergone a state of 
metamorphosis equal in every respect in its intensity to that in the 
rocks along the west coast. The presence of such distinct minerals 
as garnet, sphene, etc., in nearly all these crystalline rocks, and their 
absence, except occasionally in a fragmentary condition, in those which 
have not undergone this change, is highly important evidence, being 
indeed to the petrologist, what fossils are to the paleontologist. 
The state of all the minerals, rather than the preponderance of any, 
must perhaps be taken into consideration chiefly in these inquiries ; 
but in addition there can be no doubt that the actual development of 
minerals which could not have been present in the sediments, 
such as sphene, garnet, etc., in tolerably regulated proportions, is 
evidence clearly of the utmost value in any attempt at correlating 
the metamorphic rocks of different areas. 
[ PrrroLocicAL Remarx«s.—In the foregoing paper it will be seen 
that no rock has been regarded as a gneiss which did not contain the 
minerals quartz and one or more felspars, in an intimately crystalline 
condition. It may be observed also that the minerals sphene and 
garnet have been found to be almost universally present in rocks of 
this type from this area, the former being frequently abundant. The 
term schist has been restricted to those rocks, deficient in quartz 
but rich in mica, in which the quartz appears to have parted with its 
detrital character, and the crytalline grains have become so moulded 
together that even with the aid of polarized light it was found difficult 
to determine the original boundaries of individual grains. 
Comparing the rocks of Gaerloch and Loch Maree (Notes 1—8), 
with those of Ben Fyn (Notes 21—28), the same intimate crystalliz- 
ation of the quartz and felspar is apparent which is characteristic 
of the true gneisses, with a similar variability in the proportions of 
these constituents. They are also characterized by the presence of 
the minerals sphene and garnet, which also vary in amount. The 
former is of a pale yellow colour and in distinct crystals, is more 
abundant in the mica bands; the latter is frequently exceedingly 
