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OCR
MINERALOGICAL REMARKS. 281 ficial impreffions ; likewife polygonal with rounded angles, like the fhape that wax or clay aflumes when carelefsly rounded by the fingers, but they are all outwardly quite imooth and polifhed, and look as if they had been melted. The darker-coloured beds are not parallel to.the longer or fhorter diameter of the pebbles, but deviate from it, and run in all dire@ions ; and when the ftone breaks, it is not in the diredion of thefe apparent beds, but in indeterminate fragments, quite accidental, and with a concavo-convex and fplittry _fraéture, like foft glafs (weiches glafi). The.edges and corners do indeed cut glafs a little, but they are foon worn away. The fize of thefe pebbles is very various, and they are found from the fize of muftard or poppy-feed to that of a hafel-nut, feldom greater ; yet fometimes they are almoft as big as a walnut. This fubftance, which has all’the appearance of glafly quartz, ina moderate red heat, or before the blow-pipe, likewife begins, yet in a lefs degree, to turn white and become frothy, and changes to a fine fubftance like pumex, which may be imprefled with the nail. In heating it feems to emit a white phofphorefcent light. The fcorification hardly enters above a quarter of a line, and the internal part remains fill firm and tranfparent : if this is broken, every fragment fhews the fame appearance when heated ; commonly the external parts begin to crackle and fly before they are throughout red hot. «The other kind, which, according to the following obfervation of Surgeon Allegretti, are found in a different part of the mountain, Oo have 29
