Note 44 — ARGILLACEOUS EARTH, OR ARGILLA.

Profeſſor Bergman does not here ſeem to be ſufficiently aware of the difference between our Devonſhire pipe clay, and that which is uſed in the manufacture of porcelain. The former, in an open fire, burns to a blueiſh grey, or pidgeon colour; the latter remains white. The former ſeems to be the ſame as the Cologne and Maeſtricht pipe clay, of Cronſtedt, §78; the latter is a decayed Feldſpath, and conſequently, according to our author, (§ 130) contains magneſia. Our porcelain clay, likewiſe, has quartz, chryſtals, and mica mixed with it, parts of the granite which it originally compoſed. Before it is uſed the quartz is ſeparated, but the mica remains. I am indebted to my friend Mr. Watt for theſe obſervations. W.