Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/349

Rh Those specimens which heretofore were called native tin, are now generally believed to have been accidentally left by the smelters of the ore, and wherever it is discovered, the place may fairly be supposed to be the site of a smelting-place. It has now obtained the name of Jews-house tin.

The oxyd of tin is rarely found in Cornwall free from an admixture with other substances, but in this state it has been produced in masses of considerable size. From the mine called Polberrow in St. Agness, one block of tin ore was raised weighing 1200lbs. which produced more than one half of metal. The oxyd of tin seems to occur almost uniformly in a state of crystallization, with whatever substances it is intermingled, or however minute its portions, in the common tin-stone of the mines. It is rarely found in shapeless masses, except, indeed, the rounded grains of alluvial deposition; and even amongst these many appearances of crystallization, but mostly of the macle, may be noticed. Not only are the same crystalline forms generally apparent on each cabinet specimen, but even entire veins seem to be productive principally of the same varieties. In the tin-stone of Polgooth near St. Austle, I have rarely seen any other than minute crystals of the form of fig. 66, Pl. 18. That produced by Pednandrae, an extensive tin mine close by the town of Redruth, is almost uniformly of the macle described by fig. 208. Pl. 25. From Huel Fanny mine, which produced tin only in the shallow part of the copper vein, I have never observed any other forms than those described by figs. 108. Pl. 20. and 160. and 162. Pl. 22. and many of the crystals figured in the series of the 7th and 9th modifications, have, I believe, only been brought from Relistian mine. If it should hereafter more generally appear

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