H. COATES AND P. MACNAIR ON BANDED HORNBLENDE SCHIST. 159 
At Balhoulan Quarry the clastic rocks had, prior to their meta¬ 
morphism, been invaded by a sill of basic lava, which had subse¬ 
quently been altered in the general shearing of the rocks into a true 
hornblende schist. Seen in hand specimens, and in the face of the 
quarry, the rock is of the usual dark greyish colour, dipping at an 
angle of 30 deg. to the north-west. The most striking peculiarity of 
the rock is the presence in it of numerous bands and lenticular 
masses, showing to the naked eye a distinctly granular clastic 
structure. They vary in size from a mere line to a couple of feet in 
thickness, and lie more or less parallel with the shearing planes of the 
hornblende schist. In one instance a large lenticular mass, nearly a 
yard in diameter at the widest part and tapering down to a few inches 
near the edges, may be seen, while the more striking examples might 
be more strictly called bands rather than lenticular masses. They 
run across the face of the quarry, having an average thickness of five 
or six inches, and extending to about fifteen yards in length. As 
already remarked, in hand specimens from the larger bands and 
lenticular masses the original clastic structure of the enclosed rock 
masses in the hornblende schist can be distinctly recognised. It 
seems to have been a grit, or fine conglomerate, all the pebbles of 
which have been crushed and elongated along the line of shear. It 
will, of course, be understood that these conglomerate or grit masses 
and bands have undergone a double metamorphism,—first, that con¬ 
sequent upon their inclusion in the molten rock, the effect of which 
would probably be simply an induration of the pebbles and grains in 
the rock; and, secondly, the shearing or drawing out process which 
they would have to undergo along with the schists. 
The fragmental structure is also well shown on the surface of the 
bands, where they come in contact with the hornblende schists, the 
larger pebbles standing out all over the surface in knobs. This may 
be accounted for by supposing that the fragments of grit and conglo¬ 
merate torn from the clastic rock while the sill was being injected 
into it would be somewhat coarsely granular, or pebbly, on the surface, 
and that their enclosure in the molten lava would help to retain this 
character even after the period of the second metamorphism.* 
In Fig. I. we have given a sketch of a hand specimen of the 
banded hornblende schist from Balhoulan Quarry. It will be seen 
that the bandings consist of lighter and darker portions of the rock 
alternating with one another and of bands composed of almost 
pure quartz and felspar. The former, marked b in the sketch, and 
measuring about ’125 in. in width, are probably referable to the 
* In comparing the grit bands occurring in these hornblende schists with some 
of the highly mineralised grits of Dunoon, the identity of their origin is, we think, 
at once apparent. 
