400 THE CANADIAN NATURALIST. [Dec. 



had moreover entirely filled a small lateral braucli. The same 

 conditions are seen in the filliQcr of other veins in this vicinitv, 

 which are often much larger, and present upon their walls bands 

 of an inch or two of the yellowish feldspar with mica. 



The successive filling of a granitic vein is still more clearly 

 shown in a specimen from Sherbrooke, Nova Scotia, which I owe 

 to the kindness of Prof. H. Y. Hind. The vein, which is seen to 

 be transverse to the adherent fine-grained mica-schist, lias a 

 breadth of nearly four inches, about two-thirds of which is sym- 

 metrical, and is included between two layers, perpendicular to 

 the walls, consisting of a fine-grained mixture of white feldspar 

 and quartz, each about one-fourth of an inch thick, and marked 

 by subordinate zones, more or less quartzose. AVithin these 

 two bands is a coarser aggregate, consisting of two feldspars, with 

 some quartz and muscovite, plates of w^hich, and crystals of pink 

 orthoclase penetrate an irregular la3'^er of smoky quartz varying 

 from one-eighth to one-half an inch in diameter. This fills the 

 center of the symmetrical portion of the vein, on one side of which 

 is the mica-schist, while the other is bounded by a band of more 

 than half an inch of fine-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 fi2;ured a similar granitic vein, band- 

 ed with quartz, observed by him at Valparaiso in Chili, (Manual 

 of Geology, 1862, p. 713). -•' and has moreover maintained that 

 such granitic veins, like ordinary metalliferous lodes, are clearly 

 concretionary in their origin, and have been filled by slow and suc- 

 cessive deposits from aqueous solutions. 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 mineral- 

 ogists in the mica-schists and gneisses of New Hampshire, Mas- 

 sachusetts and Connecticut, including among other familiar 

 localities, Grafton, Acworth, lloyalston, Norwich, Goshen, Ches- 



* From U, S. Esploring Expedition, Report on the Geology, 1849, p. 570. 



