j 3 8 primitive rocks. pally ofhdrrtftbne-porphyry and felfpar-porphyry: The Newer Porphyry Formation, principally of clay porphyry : It alfo contains pitchftone-porphy- rv, pearlftone-porphyry, and obfidian-porphyry. In the older formation, there occurs no chalcedony or agate, no hornftone-balls, or diftiridt concretions. By thefe characters the two formations are diftin- guifhed from each other. The refemblance of the newer porphyry, to the neweft floetz-trap formation, is deferving of atten tion. The points of agreement are in the {tone it- felf, in the ftrudture of the rocks, in the exterior of the mountains, and in their ftratification. 6. It fometimes contains confiderable repofitories of ore ; but thefe are neither fo frequent nor fo a- bundantasthofe in the older primitive formations. The ores always occur in veins, never in beds: Gold, filver, lead, tin, copper, iron, and nianganele, occur in it ; but chiefly in the newer porphyry. The raoft confiderable mines in Hungary are in this newer porphyry *. A peculiar formation of .grey antimony ore occurs in newer porphyry at Ilmenau in the Hartz. 7. In Scotland it occurs fparingly ; in the ifland of Arran; near Blair-in-Athol, and between Dalna- cardoch and Tummel-Bridge in Perthfliire, at Gla- mofcard in the ifland of Skye, and in the Shetland Iflands. On the continent, we can trace'it from Norway nearly to the borders of the Black Sea. Thus, * According to Sonncnfchmid, many of the mines in Mexi co are fituated in porphyry.