General MoMahon — Further Remarks on Granite. 493, 



the presence of water at high temperature and alkali lowers, and 

 pressure raises, the melting-point, I said that " if we consider the 

 melting-points of the mineral constituents of granite we can hardly 

 avoid the conclusion that for the magma to have attained perfect 

 fluidity it must have reached a temperature of at least 1,200° C." 

 I went on to consider, in order to strengthen the above _vieWy 

 Vernadsky's conclusions that kyanite is transformed into sillimanite, 

 a well-known product of contact metamorphism, at a temperature of 

 1,320° to 1,380° C, and referred to Mr. George Barrow's observations 

 in the Highlands of Scotland on the sillimanite zone between the 

 kyanite and the granite. I also drew attention to his conclusions 

 that the granite that had produced this contact metamorphism must 

 have reached a higher temperature than that given by Vernadsky. 

 1,260° C, it will be observed, was the estimate I gave of the 

 temperature probably reached b}'' the Satlej granite when in a state 

 of aqueo-igneous fusion. The question of the temperature to which 

 the magma had fallen before the minerals began to crystallise 

 out, is a totally different one. I did not venture to estimate 

 this temperature in degrees of the Centigrade thermometer, but 

 said generally that the magma must have been above the red-heat. 

 There is a wide margin between 1,200° C. and 550° C. (red-heat). 

 When I said that beryl was the first of the granitic minerals to 

 crystallise, I did not imply that it began to crystallise at a temper- 

 ature of 1,200° C. All that I affirmed regarding it was that it began 

 to crystallise before the mica, felspar, and quartz which formed upon 

 it, and whilst the magma was sufficiently fluid and mobile to allow 

 the mineral to crystallise in its proper crystallographic form, without 

 being " interfered with or molested by other solid minerals," " during 

 the entire period of [its] crystallisation." Mr. Hunt apparently wishes 

 to detract from the force of the evidence referred to above, namely, 

 of the mica, felspar, and quartz having crystallised upon the beryl, 

 by remarking that muscovite and quartz are minerals that are found 

 in schists, and that they are sometimes formed at low temperatures, 

 and he cites Fouque & Levy to show that quartz may be formed at 

 a temperature of 200° C. This argument, however, does not apply 

 to the Satlej granite described by me. 



All petrologists are aware that some silvery micas and quartz can 

 be formed in what Bischof terms the ' wet way,' at comparatively 

 low temperature, but it is material to note that the Satlej granite 

 is not a metamorphic, but is an undoubtedly igneous eruptive rock. 

 As described in my paper, it cuts boldly across the Tertiary gneissose 

 granite of the Himalayas. The intruder, though probably also 

 a rock of Tertiary age, is of considerably later date than the foliated 

 rock invaded by it. It is not only the latest intrusive rock in that 

 part of the Himalayas, but it must have been erupted after the 

 strains and stresses of earth-movements had ceased to operate on 

 the rocks in that locality, for it does not itself contain the slightest 

 appearance of foliation. 



In my address I stated that the temperature of the Satlej granite 

 " must have been above that of red heat," and I went on to remark 



