. Bulletin . ge up to 2 or 3 cm. in length. Onsome of the specimens a little light blue cyanite can be distinguished, andthe sericite streaks are probably due to the alteration of that mineral. Thedark-colored bands when narrow consist of dark green hornblende with asprinkling of magnetite, but some of the wider bands have a narrow borderof coarsely crystalline hornblende 2 to 3 mm. wide along their contactswith the quartz-feldspar veinlets, w^hile their central portions are filledwith a fine-grained mixture of carbonate, hornblende, pyrrhotite, pyrite,and magnetite. oA specimen of this feldsp
. Bulletin . ge up to 2 or 3 cm. in length. Onsome of the specimens a little light blue cyanite can be distinguished, andthe sericite streaks are probably due to the alteration of that mineral. Thedark-colored bands when narrow consist of dark green hornblende with asprinkling of magnetite, but some of the wider bands have a narrow borderof coarsely crystalline hornblende 2 to 3 mm. wide along their contactswith the quartz-feldspar veinlets, w^hile their central portions are filledwith a fine-grained mixture of carbonate, hornblende, pyrrhotite, pyrite,and magnetite. oA specimen of this feldspar was submitted to Dr. E. S. Larsen, .Jr., for accuratedetermination of the maximum and minimum indices of refraction by the immer-sion method. His report is as follows: Oligoclase to andesine. Dominantlyandesine or oligoclase-andesine. 0( = 1 . 539 ± 0 . 003 to 1 . 544 ± 0 . 003> =: 1 . 546 ± 0 . 003 to 1 . 553 ± 0 . 003Extinction on the rhombic section 12%° andesine. THE GOLD MINES OF THE SCALE Feet Fig. 11.—Sketch showing distribution of vein quartz, Young Anieiiciin mine. The size of the hornhlende crystals seems to vary somewhat witlithe width of the veinlets with wliich they are in contact, and alongsome of the larger veinlets they are 1 cm. in diameter, while pris-matic crystals of tremolite, Avhich is also present, measure as much as 2 138 GEOLOGY OF THE GOLD BELT IN THE JAMES RIVER BASIN. cm. in length. Tremolite is frequently abundant near the quartz-feldsparstringers, sometimes being roughly segregated into bands, but does notappear to be an important constituent in the normal country rock. Occa-sionally elongated grains of a light brown mineral may be seen, whichunder the microscope were identified as orthorhombic amphibole. Microscopic examination of thin sections (Specs. 499, 500, and 501)shows that the principal minerals have undergone extensive alteration,and it is not always possible to say just how much of this was due to theinjection of
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