XL] GRANITES AND GRANITIC VEIN-STONES. 199 



grained granite with, yellowish-green mica, presenting large 

 crystals of feldspar near the outer margin, where it is succeeded 

 by a layer of pure smoky vitreous quartz of about the same 

 thickness, whose outer surface, against the wall, shows irregular 

 bosses or nodular masses, the depressions between which are 

 occupied by a finely granular micaceous aggregate unlike any 

 other part of the vein in texture.* This description may be 

 read in connection with the remarks in 27. 



Dana has described and figured a similar granitic vein, 

 banded with quartz, observed by him at Valparaiso in Chili 

 (Manual of Geology, 1862, p. 713),t and has moreover main- 

 tained that such granitic veins, like ordinary metalliferous 

 lodes, are clearly concretionary in their origin, and have been 

 filled by slow and successive deposits from aqueous solu- 

 tions. His testimony to the views which I have advocated in 

 this paper had been overlooked by me, or it would have been 

 noticed in 12. 



22. The numerous granitic veins so well known to miner- 

 alogists in the mica-schists and gneisses of New Hampshire, 

 Massachusetts, and Connecticut, including, among other famil- 

 iar localities, Grafton, Acworth, Eoyalston, Norwich, Goshen, 

 Chesterfield, Middletown, arid Had dam, seem, from descrip- 

 tions and from their mineral constituents, to be similar to those 

 of Maine, already mentioned. With the exception of Eoyals- 

 ton and Haddam, however, these localities are as yet only 

 known to me from specimens and descriptions. It is note- 

 worthy that at the former the finely crystallized beryls are 

 directly imbedded in vitreous quartz, and the same is the case 

 with the beryls of Acworth and the blue and green tourmalines 

 of Goshen. A remarkable example of a vein of this character 

 occurs in Buckfield, Maine, described to me by Professor Brush, 



* The banded structure is well shown in a granitic vein which I owe to Pro- 

 fessor Haughton of Trinity College, Dublin, got from Three Rock Mountain, 

 near that city. It consists of white orthoclase, with quartz and some mica 

 and garnet, and 'exhibits near the middle two bands of prisms of black tour- 

 maline pointing towards the centre, which is filled with a coarsely crystalline 

 orthoclase. 



f From U. S. Exploring Expedition, Report on the Geology, 1849, p. 570. 



