SILVER-BEARING VEINS OF MEXICO. ADDENDUM. Prof. William P. Blake describes the rocks from La Luz to San Bernabe* as "metamorphic clay-slates, quartzites and conglomerates. In some places the rocks are dioritic, either from All the metamorphism or by reason of the intrusion of dykes. formations are uplifted, and are flexed and contorted, so that the dip is variable. There is abundant evidence of pyritic mineralization, the rocks being everywhere rusty and red at the surface."+ The east-and-west vein near San Nicholas‡ is evidently a crossvein. There are actually many of these veins in the district, and, according to Prof. P. Aguilar, they probably follow the cleavageplanes of the clay-slate country-rock. The country-rock referred to as "porphyry" in the text, is principally rhyolitic-porphyry, and all veins occurring in it carry high-grade gold-ore, containing, generally, free gold, but in exceptional cases selenides and tellurides, or gold contained in the iron-pyrites. According to Prof. Blake “the chief veinstone or gangue of the veins of La Luz§ is a compact white quartz, with some calcite carrying argentite, pyrargyrite, stephanite, polybasite, miargyrite, and sometimes a little cinnabar. There is a considerable amount of disseminated iron-pyrites, and there are small quantities of galenite. At Bolenitos, the chief silver-mineral is the simple sulphide of silver (argentite)."|| In addition to the above, apophyllite may be added, which occurs in beautiful pink and white crystals in the Refugio mine. Prof. Blake, referring to the Veta Madre, says, "the vein is described as in three distinct parts, separated by country-rock or tepetate, and named blanco (24 metres); verde (15 metres), and negros (10 metres). Including the barren intervals, the aggregate width of the vein is 125 metres. The white (blanco) ores shown me consisted chiefly of quartz with disseminated silver sulphides; the black ores (negros) contained much iron-pyrites, sometimes * Trans. Inst. M.E., 1902, vol. xxiv., page 49. "Notes on the Mines and Minerals of Guanajuato," Transactions of the American Institute of Mining Engineers, 1901, vol. page Trans. Inst. M.E., 1902, vol. xxiv., page 52. , page § Ibid., page 53. || Transactions of the American Institute of Mining Engineers, 1901, vol. ¶ Trans. Inst. M.E., 1902, vol. xxiv., page 55. carrying argentite in small particles, and distinct crystals of argentite from the bottom of the shaft.' The CHAIRMAN (Mr. J. G. Weeks), in moving a vote of thanks, said that the members were once more beholden to Mr. Halse for a valuable contribution to the Transactions. Mr. M. WALTON BROWN Seconded the resolution, which was cordially approved. Mr. W. C. BLACKETT described an "Improved Offtake-socket for Coupling and Uncoupling Hauling-ropes;" as follows: * Transactions of the American Institute of Mining Engineers, 1901, vol. page Som a b |