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CORUNDUM GEMS.
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teration product of chrysolite. Such was the general view during the years following the Civil War, when the mineral resources of North Caro­lina were beginning to be actively developed.
More recently, it has come to be seen that this is only one phase of corundum occurrence, although much the most conspicuous. The investi­gation of the Geological Survey, conducted by Dr. Joseph H. Pratt,5 and Prof. Joseph Yolney Lewis," have traced several distinct associations in which corundum appears. Three of these are clearly developed in Xorth Carolina:—(1) In the crystalline schists, as long prismatic crys­tals, usually opaque, grey, pink, or blue; (2) in the decomposed chrysolite or peridotite rocks, called dunites, that intersect the schists, as igneous intrusions; the crystals often large and variously colored, but very rarely of gem quality; (3) in more or less decomposed basic rocks, with garnets, in the Cowee Valley in Macon County, where the crystals are small, in six-sided tables or to some extent rhombohedral, sometimes transparent and rich red. These last are the " Cowee rubies." The second group corresponds to the chrysolite or serpentine occurrence noted by the earlier writers; the first has been but recently distinguished with clearness from the second. It appears now, through further researches of Dr. Pratt that under this first head are again included two very different modes of geological occurrence,—one in a hornblende gneiss arising from the alteration of an igneous rock and its foliation by pressure, and the other in a true gneiss varying to a quartz schist, which has resulted from the metamorphism of sedimentary strata. These latter gneisses occur sepa­rately, extending along the crest of the Blue Eidge, at an elevation of 3000 to 4000 feet, from Eabun County, Georgia, to Clay County, N.C. The corundum appears in irregular bands in the gneiss, evidently belonging to it, and not in veins or dikes. Dr. Pratt concludes that these were originally aluminous shales, and that in the long process of meta­morphism, the alumina may have first separated as bauxite (hydrated oxide), and subsequently formed corundum bands parallel to the planes of lamination.
In all the other cases, the corundum is a product of true igneous action, having either crystallized out from a molten rock directly, or formed at the contact zones of such rock with others which it penetrated, by mutual chemical actions under the influence of great heat. The former is a frequent manner in which corundum exists. The extensive deposits lately made known in Ontario, are in a nepheline-syenite, plainly igneous in