COMMON OPAL. 237 cular cavities, in cotcmporaneous veins, or in short and thick beds. It also occurs in metalliferous veins, along with galena and blende, as in Saxony, Island of Elba, and in Bohemia; or in red ironstone veins in Saxony, hut never in considerable quantity. These veins traverse granite, gneiss, mica-slate, clay-slate, porphyry, &c. Geographic Situation. It is found in Iceland, the Faroe Islands, North of Ireland; in the Electorate of Saxony, as at Freyberg, Hu- hertsberg, Eibenstock, Johanngeorgenstadt, and Schnee- brrg; in Bohemia, as at Bleistadt, Fribus, Heinrichs- griin ; Brittany in France; Silesia; Poland; Salzburg; a t Florence in Italy ; and Telkobanya in Hungary. Uses. It is cut for ornamental purposes : thus, the green-co loured Silesian variety is sometimes cut into ring-stones; ®nd the yellow variety, which was formerly named wax- *pal and pilch-opal, is also cut and polished by jewellers. Observations. This subspecies is characterised by its peculiar milk- wlute colour, strong lustre, perfect conchoidal fracture, considerable transparency, and its low degree of liard- “ess and weight. Third