l6o TRANSACTIONS—PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
shearing and segregation of the original felspar and hornblende 
crystals of the rock, and are characterised by the predominance of 
some of these two minerals, the increase of felspar causing the lighter 
bandings, and that of hornblende the darker ones. The pure white 
bands marked a in the sketch, and measuring from ‘0625 in. to -25 
in. in width, are the finely drawn out or sheared representatives of 
parts of the fragmental rock caught up while the hornblende schists 
were in a molten state. That this is so was clearly borne out by their 
behaviour when being prepared for microscopic slides, for in the pro¬ 
cess of being rubbed down they separated out into large grains, just 
Fig:. I. Hand specimen of Banded Hornblende Schist from Balhoulan Quarry. 
like a clastic rock. These bands vary through all widths up to the 
large ones seven inches wide, shown in Plate I., and through that into 
large lenticular masses. These bands may often be seen to terminate 
suddenly, which fact also points to their original existence as in¬ 
clusions in the rock mass. 
We may here note in passing the peculiar phenomenon of the 
association of these sills of hornblende schist with bands of limestone. 
One of the authors has already described a striking illustration of this 
in the valleys of Loch Tay and Loch Earn,^ and it is also common in 
the extensive area occupied by these hornblende schists in Argyll- 
Trans. Geol. Soc, of Glasgoto, Vol. X., p. 302. 
