3 o 6 CLAY GENUS. Ufe. As it forms a pafte with water, and can be baked without cracking, it is ufed in potteries, for the ma nufacture of the common kinds of earthen ware. It is alfo made into bricks and tiles, and is ufed in founderies for lining crucibles to preferve them from fufion; in fmelting houfes, to aflift the fufion of cal- carious ores; and by the agricuiturift for the im proving of Tandy foils. Obfsrvation. It is compofed of the fined: part of the detritus of decompofing rocks, as of granite, gneifs, por-' phyry, &c. which is wafhed down by great rains and floods, and afterwards depofited in ftill places* third
