H. COATES AND P. MACNAIR ON BANDED HORNBLENDE SCHIST. 155 
inch in thickness, and sometimes corrugated into a series of fine 
foldings. Mineralogically, these bands were composed of alternating 
layers of granular quartz and felspar, and we thought they might have 
been in some way referable to the crushing of the original constituents 
of the rock. Of course it would be difficult to conceive how such a 
banded structure could have been developed, by shearing, out of a 
homogeneous crystalline rock, and in a paper read before the Glasgow 
Geological Society, on the altered Basic Rocks of the Southern 
Highlands as exemplified by the sill of hornblende schist underlying 
the Loch Tay limestone,* one of the authors has sought an expla¬ 
nation of the problem on the supposition that such bandings might 
be accounted for by supposing them to represent the ultimate 
deformation of such porphyritic hornblende schists as are found 
more or less commonly amongst these rocks. That this may be the 
case in some instances is highly probable, but the phenomena seen at 
Balhoulan Quarry open up another line of inquiry which may be of 
some value in illustrating the theory advanced by Mr. Teall to account 
for the banded structures in sheared igneous rocks by supposing them 
to be developed out of a heterogeneous mass of crystalline igneous 
rock during the process of shearing and metamorphism. 
It is particularly in the district of the Lizard in Cornwall that 
such altered igneous rocks as hornblende schist have to any extent 
been studied. We believe that the phenomena seen there are some¬ 
what similar to those presented by the hornblende schists of the 
Scottish Highlands, and we therefore propose to cite briefly the 
various theories that have been advanced to account for these 
banded hornblende schists as seen at the Lizard. 
In his original papers, and up to that published by himself and 
Major-General McMahon in 1891,! Professor Bonney maintained 
that the banding, and more particularly the current bedding which 
he described as occurring in these rocks, were only to be accounted 
for on the supposition that the rocks were of stratified origin, though 
they were probably of volcanic nature, being ejected as tuffs from a 
volcanic vent. In his later papers,—namely, that on the ‘‘ Horn¬ 
blende-schists, Gneisses, and other Crystalline Rocks of Sark ” | and 
the “Serpentine, Gneissoid, and Hornblende Rocks of the Lizard 
District,”§—Professor Bonney withdraws from his original position 
in which he believed these rocks to be of pyro-clastic origin, and, 
while still opposing the dynamo-metamorphic theory, he advances 
the idea that the banding may have been caused by fluxional move¬ 
ment in the yet unconsolidated magma of basic igneous material. 
■" Trails. Geol. Soc. of Glasgow., Vol. X., p. 302. 
fFor these papers see Quart. Jour. Geol. Soc. 
X Quart. Jour. Geol. Soc., Vol. XLVIII., page 137. 
§ Quart. Jour. Geol. Soc., Vol. LII., page 21. 
