Pseudo-Volcanoes. It may excite furprife that I have faid fo little regarding the different productions of volcanoes, after the numerous works that have been publifh- ed on this fubjedt. I have only to fay, that the defcriptions hitherto publifhed are in general fo vague and imperfedt, that it is not poffible, from them, to give a fatisfadtory account of the various true volcanic rocks. We have to expedt a defcription of this kind from that confummate mineralogift Mohs, one of the few capable of con ducting with judgment fo delicate and interefting an inveftigation. We fhall conclude the account of the general mineral repofitories, that is, the different kinds of rock, by dating the phenomena, and explaining the caufes, of volcanoes. __ Volcanoes are of two kinds: I. Pfeudo-Vol- canoes. 2. True Volcanoes. 1. Pfeudo-Volcanoes. 1. They occur ufually in low fituations, fome- times alfo in hilly country. They are difcovered by the fenfible heat of the furface of the earth in their vicinity ; fometimes by fmoke, more feldom by flame. Sulphureous and ammoniacal depofi- tions frequently incruft the ground ; and fome times warm fprings occur in their vicinity. a. They are almoft always fituated in the inde pendent coal formation-, and are caufed by the fpontaneous