4 22 Second Appendix. the moift way, which at firft fight may bc found to refemble it. ift, Pumice-, this of all fubftances is moft pecu- liarly appropriated to volcanos, particularly that of the firft variety; yet fometimes a compadted congeries of felfpar, and fhorl, crvftals with fome fcales of mica, have been miftaken for it; 2 Nofe. p. 183; nor is mere iloating on water a fufficient charadter whereby to diflinguifh pumice, for various porous lavas float on water; Fauj. Mineral, des Volcan. 265; fo alfo do the fcorite of fome flates which alfo have a greenifh grey cojour. 1 SaufT. 78. It fhould alfo be remem- bered, that pumice as it fioats on water may be conveyed from a great diftance. 2d, Volcantc Ajhes\ thefe, when indurated, much refemble wacken; and accordingly this lad has often been taken for them, Mr. Dolo- mieu has fallen into this miftake in bis defcription of Lipari, p. 57, as muft be evident to any irn- partial perfon that confiders it. Otbers have taken comminuted argillite for volcanic afhes. z Nofe. 158. 3d, Pouzzolana; decayed traps, or trap por- phyries, particularly when compadted with clay, much refemble pouzzolana, and often anfwer the fame purpofes; thei efore they have often, paffed for it. See 1 Nofe. 64, 65 ; a Nofe. 74. 11 ; Nev. Entd. p. 69 ; and Lefke G. 209, 221. 4th, Tufas ; wacken has been fometimes taken for thefe. 5th, Piperino; amygdaloids, out of which their kernels had fallen by decay, fometimes refemble this ftone; fo alfo do decayed traps, or bafalts. 1 Bergbau. 398.
