Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/129

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119
Mr. William Phillips on the Veins of Cornwall.

A vein is termed a caply load when consisting of a hard, compact and unpromising substance, which seems principally to be quartz intermix with minute portions of chlorite, giving a greenish, or brownish green tinge to the mass. Tin is often found in it, copper rarely. But if a branch of copper ore, or a gossan be found to take its course down the vein, it commonly makes a durable copper mine.

A vein is said to be a pryany load, when the tin or copper ore does not occur in a compact state, but when the stones containing either of them are found mixed loosely with other substances, such as gossan or flucan. Pry in the Cornish language signifies clay.

A vein that abounds in blende is called a black jack load, which is generally unpromising for tin, but is considered a good omen for copper. It is rarely found that blende continues to any considerable depth. It is also called mock-lead by miners.

Grouan[1] is the common technical term for granite, so that when a vein abounds in that substance, either in masses or blocks, or in a decomposed state, it is called a grouany load, which is rarely found except in a granite country. Grouan is more promising for tin than for copper; though veins containing the latter have often of late been found in the granitic districts of Cornwall, of which the western part of West Huel Virgin, Carharack, and Huel Damsel, all rich copper mines, are instances.

It must be remarked that veins generally take their names from the substances which abound but a little way below the surface. But, the circumstances of veins change so often, and their contents frequently participate so largely of the nature of the country they traverse, that the same appellation will not often hold for them in

  1. Grouan signifies Gravel, in the Cornish language, Borlase.—It seems therefore probable that Grouan, correctly speaking, is decomposed Granite.