/ j8a CLAY GENU9, Geognostic Situation, According to Werner, it belongs to the floetz trap formation. It generally refts on bafalt, which was to be expected from its more chemical nature. It has a great affinity to bafalt, into which indeed it fometimes paffies. Geographic Situation. It is found near Zittau in upper Lufatia; in the Bohemian Mittelgebirge, and many other places of that highly interefting country ; in South America according to Huinbold, and in the inland of Lam- laffi in the frith of Clyde, where it occurs in beauti ful and large columnar diftindt concretions. I Obfervatians. x. Very generally cryftals of felfpar are imbedded in it, and then it forms porphyry flate, a rock which is very different from porphyry, although it has been often confounded with it. 2. Dr Reufs, in his mineralogical defcription of Bohemia, mentions it as belonging to the primitive rocks; this affertion, however, is devoid of proof. twenty*
