GEOLOGICAL OCCURRENCE. 39 



position of the large masses of pegmatite cutting through the schists 

 as clean dykes may be practically that of the magma which was injected ; 

 but in some places the schists are simply infested with numberless peg- 

 matite-lenses and veins, as if the whole rock had been impregnated with 

 the pegmatite juice, and, as far as mere composition is concerned, it is 

 only necessary to introduce sufficient potash and possibly fluorine to 

 account for the alteration of the aluminous and siliceous schists, to 

 permit the formation of felspar, and to allow of its segregation with 

 quartz and mica into the lens-shaped cavities produced by crumpling 

 the schists. In our best mica-producing country we have large bodies 

 of granite, with a few unimportant contemporaneous veins, protruding 

 through mica-schists, which are full of pegmatite lenses, sheets and 

 dykes. There is evidence that the granite is younger than the schist» 

 intrusive into it and the cause apparently of a well-marked zone of 

 metamorphism. It does not seem to be a wild supposition to expect 

 that the vapours given off from such a granite-mass resembled in 

 essential respects the reagents by which Doelter acted on andalusites. 

 This mineral and its congeners, chiastolite, sillimanite and kyanite 

 frequently occur in the schists, and various stages, from the commence- 

 ment to the complete change of chiastolite into mica, are commonly 

 observed. 



There is an abundant evidence of fluorine in the district. Beside 

 the muscovite, which contains this element, fluorine occurs more abun- 

 dantly in lepidolite, fluor-spar, apatite and tourmaline. In some places, 

 Ghorunjee for example, instead of mica-schist, the pegmatites are found 

 cutting a granular quartz-rock with numerous large muscovite scales. 

 Such a rock was presumably once a quartzite ; but the granules of 

 clear quartz are far larger than is usual in a quartzite, whilst the mica 

 scales are certainly not of immediate detrital origin. The whole rock 

 has evidently been recomposed, a process not improbably connected 

 with the formation of the pegmatite. Experience teaches the pros- 

 pector to look more hopefully at the pegmatites cutting mica-schists 

 than those found in other " countries", and the circumstance suggests 

 a genetic connection. But it does not necessarily follow that the 



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