92 Of tbe FLEXIBILITY of 
but alfo a certain variety, arifing from different modifications of 
thofe conditions. Thus, for example, the plates of mica may 
be united with the particles of quartz, while thefe inflexible 
particles are not united with each other. Here is a modification 
which may alfo take place in various degrees ; for part of the 
quartzy particles may be cemented, while there is fufficient fe- 
paration upon the whole, to admit of all the flexure which is 
here perceived. 
I make little doubt that fomething of this kind is the cafe 
with the prefent example ; that is to fay, that there is a fuffi- 
cient conneétion among the parts to preferve the proper con- 
fiftency of a ftorie, and a fufficient laxity in the compofition to 
admit of many of its parts moving in relation to each other, at 
the fame time that the whole is connected. 
But if among the indefinite variety that may happen in the 
difpofition of thofe materials, and in the {till more various de- 
grees in which the cementing or confolidating operation may 
proceed, there is but one in which the greateft degree of flexi- 
bility may be admitted of, we fhall find reafon to conclude, 
that while an example equal to the prefent may be extremely 
rare, yet that upon accurate obfervation, many ftones of that 
kind may be found to poflefs fmall degrees of this fpecies of 
flexibility, fuch as might pafs unnoticed by common obferva- 
tion. 
Tue frellften or geftelifiein of the Swedes and Germans, 
which they employ for the building of furnaces, is a ftone of 
this kind, being, according to CRonsTEDT, compofed of quartz 
and mica. Let us now confider what is the quality in a ftoné 
which, befides being apyrous, is required in order to adapt it 
to that purpofe, of being durable in a furnace. It is precifely 
the fame quality that would procure a certain degree of flexibi- 
lity to the ftone. In proportion as a ftone is ‘olid and friable, 
it is improper for that purpofe. Rut in a porous ftone, there 
is alfo a certain texture that adapts it for refifling the alternate 
operations 
