Of Cellular Lava. 403 of the lize of a nut, and readily moulder by ex- pofure to thc air. At Naples they are called, Rapillenero. Dolom. p. 203. 5th, Of Volcanic Slaggs. Thcfe intirely rcfcmble the drofs of forges, they are generally red, and heavy« \ § III. Of Cellular Lava. Its colour is brown, or rcddilh brown, er greyifh black, feldom grey. Its furface, unequal, rough, and full of ca* vities. Its luftre, o. Its tranfpareney, o. Its fracturc carthy, and full of cavities. Its hardnefs, from 7 to 9. Its fp. gravlty va riable with its porofity, but does not exceed a.8. Mr. Dolomieu pretends, that its internal pores diflinguifh it from porous ftones of Neptumin origin. Notes on 3 Bergm. p. 184. Thefe pores are larger ncar the furface, than towards. the center. Ponccs, 295. It is more fubjeft to deftru£hon than compact lava; yet no compaft lava is ever found wholly deftitute of the cellular. Ponces, 277* It generally affefls the magnetic needle. D d 2 § IV*