1903-4.] Mr J. G. Goodchild on Intrusive Bocks. 219 1 
rocks would actually lift and thus conform to the upper boundary 
of the intrusion. But where the magma is more fluid, and the 
pressure to be overcome surpasses some, as yet undetermined, 
amount, solution ensues, and the process becomes a physico- 
chemical one instead of a purely mechanical act. 
At any rate, and by whatever means the process may have been 
carried out, I can confidently assure my fellow-workers that the 
replacive mode of occurrence of intrusive masses is the rule and 
not the exception. The belief founded upon these facts is by 
no means what it has lately been described — a superstitious belief 
entertained by ignorant miners, but is one that geologists in 
general will have sooner or later to accept, whether that belief is 
in accordance with preconceived ideas or not. 
Taking it for granted that the evidence of replacement is 
admitted, there next arises the question as to how the missing rock 
has been removed. Evidence bearing upon this, and helping to 
furnish some kind of answer to that question, is certainly not 
entirely wanting. It will be found in many cases that Nature 
has not always finished the work of removing the rock so neatly 
that no trace of the mode of attack can be found. Various 
stages may be seen when a large number of junctions come to be 
examined, and by patient investigation it is quite possible to- 
arrive at a tolerably good idea regarding the method that has been 
followed. A brief description of a few cases observed by myself 
may be given first, and to these may be added some observations 
made by other geologists, selected from the writings of those whose 
claim to be regarded as careful observers probably no one will 
question. Choice will be made of the phenomena at first on a 
large scale, and I shall choose the mode of attack followed by 
granite as being the most suitable for the purpose in view. One of 
the best examples is that presented by the marginal zone of the 
Ross of Mull granite. That granite rises through some ancient 
rocks of sedimentary origin, which pertain, I think, to the lower- 
part of the Highland Schists. They are chiefly greywackes and 
flaggy quartzites which had been much affected by dynamic 
metamorphism long prior to the intrusion of the granite. The 
marginal zone is one of considerable width, and is by no means a 
mere line, as one is apt to suppose is usually the case. For quitfr 
