Clay Stone. Geoznostic Situation. It forms vaft rock mafles, occurs in beds, in veins, a °d makes the bafis of clay porphyry. It is found accompanying the neweft porphyry formation, alfo in heds and veins in the independent coal formation. Geographic Situation. It is found in Saxony, as at Chemnitz, Stolberg, and the Windberg in the Plauifchen Grunde near to I^ r efden; alfo in Scotland, as in the Pentland Hills near fdinburgh, and the llland of Papa Stour, one °I the Shetlands. Obfervatiom. It pafles fometimes into potters clay, fometimes >nto flate clay, and alfo into jafper. It probably alfo pafles into compa£t felfpar ; the reafons for this fup- Pt>fition will be fully explained in the Geognofie, "'here I (hall have an opportunity of detailing feveral and interefting fads refpefting this foffil, conft- dered as conhituting a particular formation. SIXTH
