162 TRANSACTIONS—PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
mental structure of an ordinary clastic rock. The accessory minerals 
are garnets and iron ores, the former being often so numerous as to 
form a large proportion of the bulk of the rock. They seem to be 
more numerous along the bands of felspar and quartz than along 
those of hornblnde, which would favour the idea that the felspar in 
the process of shearing may have ultimately passed into garnet. The 
prisms of hornblende are seen to lie with their longer axes in the 
direction of the shearing force, and parallel to the bandings of the 
rock. Where they encounter the garnets they are often seen to bend 
and flow round them, thus seeming to indicate that the garnets had 
crystallised out first. 
In describing the macroscopic appearance of these rocks, we 
referred to two kinds of banding, one in which the grains of quartz 
and felspar were largely intermixed with grains and long prism-shaped 
crystals of hornblende, and another which seemed to be composed 
of fine granular quartz and felspar, without any indications of horn¬ 
blende. The former type of banding we are inclined to think may 
simply be owing to the segregation of the hornblende along certain 
zones of the rock, leaving the original quartz and felspar of the rock 
comparatively free from hornblende. Of course, vice versa^ the 
quartz and felspar would also have a tendency to segregate together 
into bands or zones. On the other hand, the bands which represent 
the fragments of the original clastic rock which were enclosed in the 
hornblende rock during its intrusion as a molten lava can easily be 
recognised by the absence of hornblende, and also by the distinctly 
granular or fragmental structure of these bands, both in hand and 
microscopic specimens.* 
In Fig. II. one of these bands is shown. It is composed 
mainly of quartz, with a pale green secondary mica, and runs parallel 
to the general schistosity of the rock. Unlike the other bandings 
just described, it is sharply defined from the surrounding hornblende 
schist. The junction of the banding with the normal rock is exceed¬ 
ingly irregular, being similar to the larger bands previously described 
in the macroscopic appearance of the rock, but on a much smaller 
scale. 
The section shown in Fig. III. is cut from one of the larger bands 
of grit included in the hornblende schist. The white eye-like or 
lenticular parts represent the original grains of quartz and felspar 
* It might be supposed that all these bands were merely the result of segrega¬ 
tion, but we are inclined to think that many of the so-called bands or veins of 
segregation found in the clastic schists of the Highlands are really the original 
quartz pebbles and boulders drawn out into long linear streaks and bands, of 
which we have seen several striking examples on the hillsides near the foot of 
Loch Eck and at Dalveich on Loch Earn. 
