A. R. Hunt — The CrystaUisation of Granite. 393 



water could not exist as a liquid, whatever the pressure ; for that, 

 as I understand it, is the meaning of the term critical temperature, 

 or critical point. 



Now, on carefully studying General McMahon's paper, I find 

 that, after deducing an approximate temperature of the Satlej magma 

 from the fusion temperatures of the individual minerals, of which 

 he tells us beryl was the first to crystallise, at a temperature 

 approaching 1,200° C, he further tells us that the beryl contains 

 water inclusions with deposited crystals, and gas inclusions. The 

 General further describes water as being held by pressure in a liquid 

 state, in the more than red-hot magma. 



These statements are not only inconsistent with the old physical 

 theory of granite, but entirely subversive of it. On reviewing my 

 paper in the light of General McMahon's address, I found that the 

 question at issue could be indirectly reduced to a single point, which 

 involved (if a point which has no magnitude can be said to involve) 

 all the others. That point is the correctness or otherwise of 

 Professor Hartley's conclusions as to the crystallisation of topaz. 

 I thought it the better plan to refer the question at once to 

 Professor Hartley, and enquire whether in the last twenty-five 

 years he had seen any reason for reconsidering his conclusions as 

 to topaz. If the answer were in the affirmative I would withdraw 

 my paper without reserve. But Professor Hartley has been good 

 enough to reply to my enquiry, and the answer is in the negative. 

 Thus I find myself once more in the hopeless situation of the crock 

 between the pot and the kettle. 



Many of the readers of the Magazine must, I am sure, be golfers, 

 and I am confident I may rely on their sympathy as being the mere 

 captain of a golf club with a couple of antiquated microscopes, and 

 far more competent to write an article on mashie approaches and 

 putting than on the consolidation of granitic minerals. They will 

 also agree that mashie approaches are far more important than fluid 

 inclusions. 



The case, however, is simple, and the evidence perhaps more 

 easily tested by the ancient microscopes than by the cheaper and 

 more popular modern ones, which often dispense with special sub-stage 

 apparatus and mechanical stage. All my petrological readers, with 

 a fair collection of slides, will have among their specimens slices 

 -containing liquid carbonic acid. If the subject is new to them, 

 I would suggest their reading Dr. Sorby's and Professor Hartley's 

 remarks on liquid carbonic acid, and having done so to treat these 

 eminent scientists at the outset with respectful scepticism. There is 

 no reason to blindly accept their testimony, because it is open to 

 any petrologist to put much of it to the proof for himself ; and it is 

 always safe to follow the example of the late William Froude, F.E.S., 

 who once described himself as a first-rate doubter. Now what we 

 gather from Messrs. Sorby and Hartley is, that in numerous minerals 

 inclusions occur containing two fluids, and that on heating the 

 specimens one fluid often disappears at or about the critical tem- 

 perature of carbonic acid. In fact, one of the fluids behaves exactly 



