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with fal fodæ. It is confequently a
filiceous mais outwardly covered with
lime, and has fixed itfelf on the following
fubftance.
8, A folid irregular plated and
broken cruft, o f a dark colour, but in
many places tinged with bright blue
ipots. It becomes quite fmooth in
cutting, almoil like ilone marie, but
does'not crumble in water, nor does
it become foft in it ; with acid it fliews
an eftervefcence which foon ceafes ;
with the blow-pipe it grows hard,
fcarcely melts at the thinneil edges,
and is attacked with fome motion both
by borax and fufible urinous fait and
fal fodæ, but is not entirely diíTolved
by any o f them.
9, The fubftance found at the bottom
of the brook, which carries off*
the water that guflies out, is brown,
fpongy, and compofed of pretty hard
flakes and threads, that are covered
with fine glaíTy cryilallizations. Thefe
are clear only in fome few places ; but
lofe their brown colour, both in fire
and marine acid, and become quite
clear.
The
The fmall cryftals pu i f up very
much under the blow-pipe, almoil like
borax ; they float in bubbles on the
furface, and are diffolved with great
difficulty by borax ; they are attacked
by fal fodæ with a flrong ebullition : it
is the fame with the more folid flakes,
but they do not puff up fo ftrongly as
the cryilallization. Thefe feveral qualities
here mentioned evidently ihew,
that this cruftated ftone confifts o f
zeolite.
10. From Reykum you fent me
calcareous fpar in lumps, that are
externally rounded, as i f they had
been toifed backwards and forwards
by the water, and rubbed againft hard
bodies.. In them there are fmail
greyiib green cryftallizations, that
diifolve by the blow-pipe to a black
flag ; the fal fodæ makes them eifer-
vefce a little, but does not diifolve
them ; they are likewife attacked with
fome emotion by fufible urinous fait.
1 1 . A loofe, tubulofe, whitifli cruftated
ftone, or cavernous incruftation,
and with impreftions o f leaves,
ftalks,