H. COATES AND P. MACNAIR ON BANDED HORNBLENDE SCHIST. 157 
be seen in a slice mounted on an ordinary microscopic slide. 
The supposition that these bands were originally thick and were 
drawn out into streaks of thread-like thinness by stretching is not 
supported by the microscopic evidence, and fails to explain how the 
hornblende segregated into a series of parallel zones. He further 
asks the question, in advancing his own theory. How has this segre¬ 
gation of the hornblende been produced ? Accepting, to begin with, 
the original volcanic ash-bed origin of these rocks, he proceeds to 
show how, by the percolation of heated water through these ash-beds, 
not only the ordinary types, but the banded hornblende schists might 
be produced. We cannot now enter into the details of this theory, but 
shall only quote the conclusion he arrives at. He says :—“I suppose, 
then, to conclude my remarks on this branch of the subject, that the 
banding of the hornblende schists was produced by the capillary flow 
or percolation of heated water through the rocks in two ways, namely, 
by the leeching out of unstable minerals (such as pyroxene) from the 
spaces between the planes of lamination, and by the formation of com¬ 
paratively stable minerals (such as hornblende) along those planes.” 
In a paper published in the Quarterly Journal for 1893, Messrs. 
Fox and Teall* deal with certain sections of the Lizard rocks. They 
there come to the conclusion that the serpentine and hornblende 
schists of the Lizard are part of the same igneous complex, and that 
the latter rocks, like the former, are undoubtedly of truly igneous origin. 
They do not deal with the problem of their banding, but simply state 
that the banding had taken place prior to their folding and corrugation. 
In the neighbourhood of Pitlochry, numerous sills of hornblende 
schist occur, though it is in Balhoulan Quarry alone that we have 
been able to see the phenomena about to be described. Numerous 
sills of hornblende schist are also exposed along the sides of Ben 
Vrackie, and are seen here and there on the road leading across the 
, hills from Pitlochry to Kirkmichael, dipping at high angles to the 
north-west. In the wild and romantic Pass of Killiecrankie and in 
the bed of the river Garry similar sills of hornblende schist also 
occur. Several striking examples may be seen in the bed of the river 
Tummel below Clunie Bridge, about half-a-mile above Pitlochry. In 
certain instances these hornblende schists show traces of an originally 
porphyritic structure, and numerous boulders of these are found in 
the bed of the Garry. Professor T. G. Bonney thus describes one of 
these in a paper on “ Some Schistose Greenstones and allied Horn¬ 
blende Schists from the Pennine Alps, as illustrative of the effects of 
Pressure Metamorphism.” f In a foot-note referring to the Scottish 
example, he says, “Since the above paper was written I have obtained 
* Qiiar. Jour. GeoL Soc., Vol. XLIX., p. 199. 
^ Qziart. Jotu\ GeoL Soc,, VoL XLIX. 
