200 Proceedings of Royal Society of Edinburgh. [sess. 
of the sedimentary strata, and not to displace them, leaving them 
pushed out on all sides. If we suppose the intruded rock to eat 
its way into the sedimentary strata, assimilating portions of it, 
we allow a good deal of what is asked by those who hold the 
metamorphic origin of granite rocks, i.e ., the possibility of changing 
a sedimentary into a granitoid rock. The advocates of that theory 
may take their stand upon the assimilated portion, and ask is it 
the heat of the intruded mass, or the new conditions under which 
the minerals have been brought into contact with the sedimentary 
rocks, which has produced the change, and then point out that 
both the one and the other may be obtained by a sufficient 
depression of the sedimentary rocks ” [the above italics are the 
author’s]. 
In a later reference, made in the Geological Survey Memoir 
on 98 S.E., pp. 41-42, the same author repeats the statement 
chiefly with reference, on this occasion, to the dykes of minette, 
porphyrite, and quartz felsite which occur in the region described. 
He adds the remark : “It may be worth consideration whether in 
some cases it might not be possible that the action of gases or 
of hot water holding minerals in solution, communicating along 
lines of fissure with the joints, might produce the phenomena 
observed.” 
As I happened to be working with the author at the time when 
both of these remarks were penned, and had abundant opportunities, 
then and on later occasions, of observing the facts upon which 
his conclusions were based, I can confirm them in every particular. 
Attention may be directed to the fact that no mention was made 
of any lithological passage from that of the dyke to the country 
rock. Nevertheless, in the discussions which followed the 
publication of the above passages, only side issues were raised, 
mainly on the ground that no evidence of a lithological passage 
could be made out ; and the statements of fact, thus apparently 
discredited, were allowed to drop out of sight. 
In 1879 Mr Clough of the Geological Survey took up the 
matter again, in connection with the Whin Sill of Teesdale, and 
read a paper before the Geological Society of London, in which 
similar views were advanced, and supported by an excellent array 
of facts and arguments. Again a side issue was raised, and the 
