Title: Annual report of the Board of Regents of the Smithsonian Institution
Identifier: annualreportofbo1899smit (find matches)
Year: 1846 (1840s)
Authors: Smithsonian Institution. Board of Regents; United States National Museum. Report of the U. S. National Museum; Smithsonian Institution. Report of the Secretary
Subjects: Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science
Publisher: Washington : Smithsonian Institution
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Smithsonian Libraries

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288 EEPORT OF NATIONAL MUSEUM, 1899. up, and interrupted here and there iDy belts of later formation. Mica veins are found iTere, in fact may be said to char- acterize this horizon everywhere, from its eastern outcrop, near the seaboard, to and quite under the flanks of the Smoky Mountains. It is, however, in the great plateau of the west, between the Blue Ridge and the Smoky, that the mica veins reach their greatest development, and have given rise to a very new and profitable industry,—new and at the same time very old. It may be stated as a very gen- eral, almost universal, fact, that the mica vein is a bedded vein. Its position (as to strike and dip) is dependent on and controlled by, and quite nearly conformable to, that of the rocks in which it occurs, and hence, as well as on account of their great size, some observers, accustomed to the study of veins and dikes and the characters of intrusive rocks in other regions, have been disposed to question the vein character of these masses at first. But a good exposure of a sin- gle one of them is generally suffi- cient to remove all doubt on this score. The mica vein is simply and always a dike of very coarse granite. It is of any size and shape, from a few inches—generally a few feet— to many rods (in some cases several hundred feet) in thickness, and in length from a few rods to many hundred yards, extending in some cases to half a mile or more. The strike, like that of the inclosing rocks, is generally northeast, and the dip southeast, at a pretty high angle; but they are subject, in these respects, to many and great local variations, all the conditions being occasionally changed, or even re- versed. An idea may be formed of the coarseness of these veins from this statement, that the masses of cleavable feldspar and of quartz (limpid, pale yellow, brown, or, more generally, slightly smoky), and of mica, are often found to measure several yards in two or three of their dimen- sions, and weighing several tons. I have a feldspar crystal from one of these mines
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