Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/127

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117
Mr. William Phillips on the Veins of Cornwall.

Denominations of Metalliferous Veins.

The substances which form the contents of the metalliferous veins differ very materially; nor are veins distinguished simply by the name of the ore for which they are wrought, as a Copper Load, or a Tin Load; but they have obtained various appellations, according to the nature of the substances found to predominate in them. For as the greater proportion of the contents of most of them, is neither the ore of copper nor that of tin, the miner in speaking of them, gives them the appellation which is technically descriptive of the vein-stones:—as a gossany, sparry, mundicky, peachy, flucany, scovan, caply, pryany, black jack, and a grouany Load.

Gossan is a friable ferruginous substance, consisting generally of clay, or of some siliceous matter of a loose texture, coated or tinged with iron, in various proportions, arising probably from the decomposition of pyrites; it varies in colour, from pale yellow to deep red, sometimes inclining to black. A Gossany Lode is more common than any other, and most promising both for tin and copper. Gossan has been plentifully found at small depths in many mines that produced considerable quantities of one or the other metals, both beneath as well as mingled with it; as of tin in Huel Sparnon and Pednandrae, and of copper in Huel Gorland, and in East and West Huel Virgin.

When the load or contents of a vein is termed sparry, this does not imply that it is of solid spar or quartz, but that quartz predominates. A vein in which this substance is considerably compact is very unpromising; and if at the same time the vein becomes narrower as it descends, it is generally relinquished as a hopeless undertaking; which was the case in Huel Gorland, as noticed in my memoir on the red oxide of copper.[1] A vein abounding in fluate of lime

  1. Geological Transactions, vol.1.