92 Of the FLEXIBILI7T 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 connection among the parts to preferve the proper con- 

 fiftency of a florie, 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 flill 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 poffefs fmall degrees of this fpecies of 

 flexibility, fuch as might pafs unnoticed by common obferva- 

 tion. 



The Jlelljlen or gejhlljte'in of the Swedes and Germans, 

 which they employ for the building of furnaces, is a (tone of 

 this kind, being, according to Cronstedt, compofed of quartz 

 and mica. Let us now confider what is the quality in a ftone 

 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. Put in a porous ftone, there 

 is alfo a certain texture that adapts it for refining the alternate 



operations 



