P. MACNAIR ON ROCKS OF HIGHLAND PERTHSHIRE. 183 
It was in the district of the Lizard, in Cornwall, that these horn¬ 
blende schists were first studied in detail by Prof. Bonney. In his 
earlier papers on this district. Prof. Bonney expressed the belief 
that these rocks were of aqueo-volcanic origin, and that the planes 
of foliation corresponded to the original planes of sedimentation. 
He even thought that he could detect in them lines of current 
bedding. In a paper giving the results of a re-examination of these 
rocks by Prof. Bonney and Major-General C. G. M‘Mahon, and 
published in the Quarterly Journal of the Geological Society for 
1891,’-® the authors admit that the hornblende schists are, in part at 
least, of igneous origin, and explain their banded structure by move¬ 
ments in the mass previous to consolidation, these views being more 
fully developed in subsequent papers. 
Perhaps the most important of all the later contributions made 
towards the study of these rocks, and one from which we may date 
the beginning of the more recent researches into their structure and 
origin, is a valuable paper by Mr. J. J. H. Teall, contributed to the 
Geological Society of London in the year 1885.^^ In this paper 
he shows that two more or less parallel dykes intruded into the 
archsean gneiss of Western Sutherlandshire have been altered from 
their original structure as an intrusive dolerite into a hornblende 
schist, and that this alteration had taken place after the dolerite 
had become consolidated, the change having been brought about by 
dynamo-metamorphism. He shows that even in hand specimens 
taken from this dyke a distinct passage can be traced from the 
dolerite into the hornblende schist. The following may be taken 
as a summary of the results arrived at in the paper:—(i) That the 
hornblende schist has been developed from a dolerite by causes 
operating after the consolidation of the dolerite, and that the meta¬ 
morphism has been accompanied by a molecular re-arrangement of 
the augite and felspar; (2) that the molecular re-arrangement has in 
certain cases taken place without the development of foliation; and 
(3) that the plasticity which has led to the development of foliation 
is that due to high pressure at ordinary temperature. 
In the year 1887 another important contribution towards the 
study of these rocks was published in the Geological Magazine^ ^ by 
Mr. J. J. H. Teall, in which he proposed to account for the banded 
structure seen in certain gneisses of the Lizard, on the hypothesis 
that they had been originally igneous rocks associated together as 
a plutonic complex. As I have already during this session, along 
with your President, Mr. H. Coates, discussed the application of 
this theory to a particular instance seen at Balhoulan Quarry, Pit¬ 
lochry, it will be unnecessary for me to enter into any further 
description of the theory, and it will be sufficient to refer you to the 
