Vol. 51.] GKANOPHYRE AND THE GRAINSGILL GKEISE1T. 143 



minerals characteristic of the true greisens are absent, and argent- 

 iferous galena is found. .Arzruni gives a long list of other minerals 

 from the mines of Beresowsk and neighbourhood, 1 only a few of 

 which are known in our area. The beresite is the ' country ' rock 

 of the gold of the Urals. 2 



These Russian beresites form a system of broad bands, the relation 

 of which to the normal granite of the district has not been clearly 

 set forth. In the case of the Grainsgill rock the field-relations are 

 scarcely open to question. The granite and the greisen form parts 

 of a single intrusive body, and there is a transition, at first gradual, 

 but ultimately more or less abrupt, from the former rock to the 

 latter. The appearance is therefore as if the greisen had been 

 ' extruded ' from the granite, and a comparison is at once suggested 

 with pegmatites such as those described by Mr. Barrow 3 in asso- 

 ciation with the igneous gneisses of Forfarshire and the neigh- 

 bouring counties. Although these Highland rocks are richly 

 felspathic, while the Cumberland greisen is almost free from felspar, 

 a comparison of specimens brings out some curious points common 

 to the two, such as the plumose arrangement of white mica which 

 Mr. Barrow considers characteristic of his pegmatites. Again, the 

 description of the Grainsgill rock given above has already suggested 

 that the abundant minute flakes of mica may have been produced, 

 in conjunction with quartz, by the destruction of felspar once present 

 in the rock. The large flakes and plumose aggregates of mica, the 

 porphyritic grains of quartz, and some other peculiarities which 

 must date from the epoch of consolidation, preclude the supposition 

 that the greisen is merely normal Skiddaw granite transformed by 

 secondary metasomatic changes or by the agency of mineralizers ' as 

 a last phase of the igneous activity ; but it is at least a tenable idea 

 that the Grainsgill rock bears the same relation to a pegmatite of the 

 Forfarshire type that the Cornish greisen does to its associated 

 granite. 



However this may be, it is significant to note, in another district, 

 a greisen like that of Grainsgill and a pegmatite like those of 

 Forfarshire occurring together and holding identical relations 

 towards the granite, with which both are intimately connected 

 During a recent visit to the Isle of Man, I had an opportunity, in 

 company with my friend Mr. G. W. Lamplugh, of examining the 

 granite of Foxdale. This rock, also intruded among Skiddaw Slates, 

 is a muscovite-granite identical with some of the Leinster granites, 

 on the axis of which it occurs. It consists of quartz, microcline, an 

 acid plagioclase, muscovite, subordinate biotite, and little crystals 

 of garnet and zircon. In the marginal part of the intrusion are 

 developed bands and masses of pegmatite, thick veins and bands of 



1 See list by Kokscharow in Murchison's ' Geology of Russia,' vol. i. App. E 

 (1845), pp. (i40-.645; also H. Louis, 'On the Mode of Occurrence of Gold,' 

 Mineral. Mag. vol. x. (1893) pp. 241-247. 



2 See Murcliison, De Verneuil, and Keysei-ling, ' Geology of Eussia and the 

 "Ural Mountains,' vol. i. (1845) pp. 47fi, 477. 



■■> Geol. Mag. 1892, pp. 64, 05 ; Quart. Journ. Geol. Soc. vol. xlix. (1893, 

 pp. 33U-337. 



ii2 



