General McMahon — Further Remarks on Granite. 495 



foreground, as I have sometimes seen, the figure of a sportsman 

 firing at a duck or pheasant, and the bird falling to the ground 

 with a broken wing and with feathers scattered in the air. The 

 majority of those who examine such a picture would altogether 

 overlook the beauty and poetry of the landscape, and would carry 

 away the idea that the object of the artist was to illustrate the 

 cruelty of sport. I think that some scientific writers labour under 

 a want of the artistic sense. They leave their meaning obscure, not 

 only by the want of lucidit}'^ of mind, but by scattering the attention 

 of their readers, by diverting them to subjects beside the real point 

 at issue. To prevent any further misapprehension I may mention 

 that I abstained for a similar reason from entering into the question 

 of what is implied by water being held in solution by granite. 



Ostwald, in his remarkable work on solutions, has enlarged upon 

 the theory that a substance in solution is split into its ions. This 

 theory has, I think, been accepted as a good working hypothesis 

 by the majority of chemists, as it clears up many points not otherwise 

 capable of explanation. According to this theory water held in 

 solution by a molten granite would be split into its ions, hydrogen 

 and oxygen, and questions regarding the critical point of water 

 would be held in abeyance during the time it was so held in solution. 

 As, however, I did not, for the sake of simplicity, treat the subject 

 in my address from the ion point of view, 1 will not attempt to do 

 so now, but shall be content to regard the water in a granite above 

 the critical temperature, as water in its gaseous state, though it must 

 be remembered that if we regard it as a gas we must accede 

 to it the kinetic energy and motion proper to a gas at a high 

 temperature. 



Mr. Hunt in his paper has come to the conclusion that " ordinary 

 granites crystallised about the critical temperature of water," and 

 in his paper on vein-quartz above referred to he records his con- 

 viction at p. 214 that "Fluid inclusions with deposited crystals 

 are clear proof that the fluid was entangled in the quartz or other 

 mineral, under 342° C." This conclusion or rule appears to me to be 

 based on two assumptions, both of which I think erroneous. The 

 first is that water enclosed in the minerals of an igneous rock was 

 enclosed after it had assumed a fluid state. The second fbllows 

 naturally from this, namely, that the mineral which enclosed the 

 fluid water must have crystallised below the critical temperature. 

 The main fallacy which underlies the above rule seems to me to 

 have arisen from Mr. Hunt's failure to realise the possibility of 

 molecules, on their coming together to form a crystal, bringing down 

 entangled with them the molecules of a gas. My critic's conclusion 

 is irreconcilable with the facts stated in my Belfast address, hence 

 possibly his anxiety to discredit my facts under cover of an attack 

 on the views expressed by me. 



I have been led by the evidence supplied me by the study 

 of thin slices to believe that the crystallisation of minerals in 

 a plutonic rock, such as granite, was a slow and gradual process. 

 I do not see how we can avoid this conclusion in the case of lar^e 



