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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 appear¬
ance 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
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