340° Messrs. Clough, Crampton, and Flett— 
riebeckite gneiss and the albite gneiss occur, is a biotite gneiss. Other 
fine-grained gneisses, which contain muscovite but little or no biotite, 
probably represent foliated aplites. 
The history of the foliation in the orthogneisses is intimately 
connected with the history of the foliation in the schists, but in the 
former there is very complete proof that this structure was developed 
after the igneous rocks were quite solid. Although sometimes nearly 
normal granites, gabbros, etc., they generally show some indication of 
deformation. In the porphyritic types the phenocrysts of quartz and 
felspar are usually less sheared than the matrix, which must con- 
sequently have been solid before the rock was crushed. The quartz 
breaks down more readily than the felspar, and every stage of 
granulitization can be made out. Where a plexus of acid veins 
permeates the basic rocks, the latter, though older, are never in 
a different state from the granites, that is to say, there is no evidence 
that the basic rocks were foliated before the granite invaded them (as 
is often seen in the Lizard district). Sometimes a complex of this sort 
has been pulled or rolled out into a banded gneiss, not unlike some 
types of the Lewisian, but both acid and basic rocks are in the same 
state, and the derivation of such a gneiss from an intrusion breccia can 
be followed step by step in the field. The crushing and consequent 
development of foliation vary considerably in intensity from point to 
point, and sometimes suddenly along certain lines of thrust or special 
shearing, which frequently strike N.N.W. But for the most part the 
foliation maintains the N.N.E. trend, which is characteristic of the 
Moine schists of this area also, and often strikes across the boundary 
with the schists. Another fact of especial significance is that the big 
masses of granite, and also the thin veins in the paraschists, are in 
a number of places foliated across their length, with the same foliation 
as marks the rocks around them.* 
The sedimentary schists that form the country rock are arranged in 
a fold with its major axis striking N.N.E., nearly parallel to the 
lengths of the granite masses, and away from the augen gneiss they 
differ in no respect from Moine schists and gneisses in other parts of 
Scotland. We may distinguish two main types—(1) the siliceous or 
psammitic schists and gneisses, with both muscovite and biotite, 
(2) coarse pelitic or semipelitic garnetiferous mica schists. Thin 
bands of zoisite-hornblende gneiss and of granulite with prisms of 
zoisite nearly an inch long are also found. The whole of these schists, 
as is well known, were originally sedimentary rocks (arkoses, shales, 
marls and sandstones), and with them occur dark hornblende chlorite 
schists which represent basic igneous masses in a state of complete 
metamorphism. In these rocks the traces of original clastic or igneous 
structures have often been effaced, though relics of pebbles of quartz 
and felspar in the psammitic gneisses locally betray their sedimentary 
origin ; the quartz pebbles are often dragged out into long ribbons. 
There are moreover in these Moine rocks no minerals of thermal origin 
1 This was first made out by Dr. B. N. Peach at the edges of the Loch Luichart 
outcrops, and was mentioned by him in the Summary of Progress of the Geological 
Survey for 1898, p. 9. 
a 
