Veins. ‘ 4 49 We can eafily diftinguilh the relative age of the different minerals contained in this formation. Quartz is almoft always the oldeft, being gene rally depofited immediately upon the walls of the vein. ' The lides of the drufes are formed of Cryftals of quartz. Upon and in thefe fides or walls, reft black-blende, arfenic-py rites, lead-glance, and iron-pyrites. It appears, that the blende and the arfenic-pyrites are rather older than the others. Upon thefe refts brown-fpar; above it we have the three fpecies of filver-ore already mentioned, viz. brittle Jilver-glancc, red Jilver-ore, and white Jilver-ore, with a fmall portion of lead-glance, and fometimes a little common iron-pyrites: of thefe five fubftances, the lead-glance appears to be the oldeft, and the three ores of filver ap pear to be of cotemporaneous formation. Thefe ores of filver are fometimes covered by fmall cryftals of quartz. Calcfpar appears laft, and- is the neweft foffil of the formation ; it is al ways in the middle of the vein, and when drufes occur, it always covers the other foflils that line their fides. Plumofe antimony occurs but rarely in this formation, and is always In drufes,—a fadt which fhews that it is one of the neweft foflils of the formation. Werner is of opinion, that it was contained in the fame folution with the five filver ores, but was precipitated laft. Although the minerals that compofe this forma tion almoft always occur together, and in the fame veins, it fometimes happens, that the black-blende, Vol. III. I i arfenic-