90 Of the FLEXIBILITY of 
tum ; and this appearance likewife proceeds from the fame kind 
of fpecular longitudinal plates, arranged in the fame order. 
I now beftowed fome pains in endeavouring to difcover, by 
the power of the lens, what was the nature of thofe reflecting 
fpecular laminz ; but I could not fay affyredly, that there were 
two different fubftances in the conftru€tion of this ftone. The 
irregular quartzy particles, and thefe fpecular bodies, feemed 
both to be of a perfectly tranfparent cryftalline-like matter. I 
then had recourfe to the blow-pipe, in order to refolve my 
doubts ; and this indeed foon made a diftinétion of the diffe- 
rent fubftances contained in this ftratum. Where the fragment 
of the ftone had received the intenfe heat of the flame, the fo- 
liated fpecular ftructure totally difappeared ; and here the irre- 
gular quartzy particles remained feemingly without change. 
In the other part of the fragment, which had been heated to 
incandefcence, the doubt with regard to the fpecular bodies 
was entirely removed, and the tranfparent mica had now af- 
fumed its natural appearance ; it had become opake with regard 
to the tranfmiffion of light, at leaft comparatively, and it gave 
an argentine appearance by reflection, as may be perceived in 
the fpecimens which I have here laid before the Society. 
I now could fee, moft evidently, the connection of the ir- 
‘regular ftruGture of the quartzy particles, with thofe ftratified 
parallel plates of mica; and I alfo underftood the reafon why 
I could not before diftinguifh the proper connection of-thofe 
two fubftances, which was no other than their perfect tranfpa- 
rency. But being thus fatisfied of the thin flexible plates of 
mica, we may now confider the particles of quartz, which 
have little cohefion, as being bound together by thefe thin 
plates of tranfparent mica; and thefe connecting plates being 
flexible, this allows a certain motion of the rigid particles 
among themfelves, without the fragure or general feparation 
of the ftone. ; 
WERE 
