Transactions . ous ore occurs at the contact between an altered shale anda massive crystalline limestone, and both rocks have been 648 [NFLUENOE OF OOUNTRY-ROOK ON MINERAL VEINS. changed by contact metamorphism. The bedding-plane is ore-bearing only where die general dip of the rocks is disturbedby flexures. In addition to the ore found along the contact, aDumber of \ei-y Large ore-bodies have been found at some littledistance in the dolomite, though always in the same structuralposition. The ore found along the altered shaje-dolomite <-on-tacl is essentially a dry quartzose milli
Transactions . ous ore occurs at the contact between an altered shale anda massive crystalline limestone, and both rocks have been 648 [NFLUENOE OF OOUNTRY-ROOK ON MINERAL VEINS. changed by contact metamorphism. The bedding-plane is ore-bearing only where die general dip of the rocks is disturbedby flexures. In addition to the ore found along the contact, aDumber of \ei-y Large ore-bodies have been found at some littledistance in the dolomite, though always in the same structuralposition. The ore found along the altered shaje-dolomite <-on-tacl is essentially a dry quartzose milling-ore; that of thedolomite, mainly galena, with accessory sphalerite and ores are connected by pipes and stringers, and boththe field and the microscopic evidence show that they wereformed by the same solutions and at the same time. There isno escape from the conclusion that the difference in the miner-alosncal character of the ores is the result of the differentnature of the enclosing rock. Fig. 8. i h m a k h Limestone Beds of Derbyshire, with Intercalated Beds of Igneous Rock (Toadstone)Traversed by Veins. (De la Beche, Geol. Obs., p. 784.) It would be tedious to enumerate all the familiar deposits inlimestone. Those of Leadville, Colorado, and Eureka, Nevada,have been thoroughly studied and described. Tombstone,Arizona, presents quartzose veins filling fault-fissures, cuttingslightly tilted sedimentary rocks, with the workable ore-bodiesformed by replacement of limestone along bedding-planes, andpresumably by the same solutions that filled the fissures. Derbyshire.—The Derbyshire lead-mines of England are alsowell-known examples of veins carrying galena in limestone, andbarren when in the intercalated intrusive trap-rocks (toadstone).Fig. 8, from De la Beche, illustrates the occurrence of galenain the limestones above and below an intrusive sheet in one ofthe Derbyshire mines. The leader or fissure traverses the toadstone as well as the lime-rock, but it is o
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Keywords: ., bo, bookcentury1800, bookdecade1870, booksubjectmineralindustries
