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Proceedings of Poyal Society of Edinburgh. [sess. 
percentage than usual, or that it could assimilate thick beds of 
limestone without the development of any additional lime silicates, 
or that it could eat up shales wbthout any perceptible increase in 
alumina-silicates being evident in any part of the invading rock. 
It must occur to any reasoning person, however, that the 
facts, at least, either do exist as stated, or they do not. If they 
do, then it is very illogical to close our eyes to them. It would be 
much better to face those facts at once, and either to accept them 
as such without attempting to explain how they came about, or 
else to re-examine the evidence and endeavour to frame some 
hypothesis which would harmonise what is known about them ; 
or, at least, to think out some explanation which would serve for 
the time being as a working hypothesis until a better one could 
be suggested. 
Bearing these considerations in mind, I have collected much 
additional evidence which bears upon this controverted question. 
Most of the facts have been obtained in the Lowlands of Scotland, 
and I have aimed, as much as possible, at citing instances which 
are either to be seen without difficulty in such easily- visited 
localities as the Queen’s Park, or else at other places within a 
short distance of Edinburgh. The behaviour of basic intrusive 
rocks Avill be considered first, taking sills in the first place and 
dykes next. 
In view of the fact that many geologists think that mechanical 
disturbance always accompanies the intrusion of eruptive masses, 
I have thought it well to give first an outline drawing (fig. 1) 
taken from a photograph by Mr A. G. Stenhouse, F.G.S., 
of the well-known example in the quarry at the south end of 
the foot of Salisbury Crags, which is the example illustrated in 
Hay Cunningham’s Eig. 3, Plate III., Mem. Wern. Soc., vol. vii. 
In this case a wedge of dolerite has been, so to speak, arrested 
wdiile in the act of forcing off a fragment of one of the beds of 
Cornstone there. The section to the left of the wedge follows 
the method of attack usual in such cases. Fig. 2, traced from a 
photograph taken at Hound Point, Dalmeny, by the well-known 
vulcanologist Dr Tempest Anderson, shows a similar wedging off 
of the country rock by the intrusive mass, which in this case is 
also a dolerite. It may be remarked that within six feet of this- 
