Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/181

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A very singular and very anomalous combination of tin with sulphuret of lead is found in the mine of Heavas in the parish of St. Mewan. There is also a vein at Marienberg in Saxony, in one part of which ores of tin are found, and in another, ores of silver. Are we to infer, that in some cases the tin veins already formed have been rent, and the new fissures filled with ore of a later formation; or are we to admit, that there are tin formations of different ages?

The cobalt united with tin, found in Wherry mine in the parish of Madron, belongs very probably to the oldest formation of cobalt, the same as that of Gieren in Silesia, which is in a mountain of mica-slate; for the veins of cobalt in secondary mountains are of very recent formation.

The tin is accompanied with arsenical pyrites, copper pyrites, and even blende, as in the mine of Trevascus. Arsenical pyrites, according to Werner, is of very old formation, although produced at different ages; for we find it (he says) with tin, with galena, sometimes, though rarely, with copper pyrites, and also with arsenical silver ore. It is not usual, he adds, to find copper pyrites with blende, but very frequently this last accompanies galena.

Copper occurs in various forms in Cornwall, independently of its combinations with tin, with cobalt, and with silver: viz. in the native state, in the states of red oxide, blue carbonate, green carbonate, sulphured, grey antimoniated ore, and arseniate. The substances