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COMMON CALCEDONY. 205 amygdaloid, and in primitive porphyry. The beds oc cur in primitive porphyry, but more abundantly, m floetz-trap rocks, as in amygdaloid, basalt, greenstone, &c. The veins are of two kinds: agate veins, which occur in primitive, transition and floetz rocks ; and metalliferous veins, that occur principally in primitive and transition rocks. The agate veins contain, besides the calcedony, also (lint, hornstone, opal, and amethyst. The metallife rous veins are of three formations : In the first, the calce dony is associated with silver and lead ores, and brown-spar, as in the Saxon Erzgebirge; in Lower Hungary, and Transylvania: In the second, with brown and black ironstone, sparry ironstone, hornstone, and other fossils, as in the Saxon Erzgebirge; in Voightland ; at Hutten- berg, in Carintliia, &c.: And in the third, along with ores of copper, as in the Trevascus mine, in Cornwall. The calcedony in these veins exhibits many different external forms, as stalactitical, botryoidal, coralloidal, reniform, &c. In alluvial country, it occurs only in rolled pieces. Geographic Situation, Europe.—This mineral occurs more or less frequently in the floetz-trap rocks of Scotland. Thus, it forms co- temporaneous veins in greenstone rocks in Fifeshire; and occurs in balls, kidneys, and veins, either singly or along with other minerals forming agate, in the trap rocks of the l’entland Ilills, near Edinburgh, those in West Lo thian, Mid Lothian, East Lothian, Dumfriesshire, La narkshire, Dunbartonshire, Stirlingshire, Perthshire, An- gushire, &c. The trap rocks of Mull, Hume, Canna, Eigg and Skye, afford calcedony ; and small portions of it occur in the trap rocks of Zetland. The most sin gular varieties of English calcedony are those found in Trevascus