$8 Of the FLEXIBILITr of 



articulation, while it preferves the component particles in one 

 entire mafs, iuffers the parts to move a certain fpace in relation 

 to each other. 



But before difTecling this ftone, in order to fee upon 

 what principle it holds its flexibility, it may be proper to form 

 a diftinct idea with regard to that inflexibility or rigidity which 

 is to be found in other ftrata. 



We do not now enquire into the means employed by nature 

 for uniting the incoherent particles of which our ftrata have 

 been compofed ; it is enough to know this fact, That ftrata are 

 thus actually found, with their particles united in every pomble 

 degree, from the flighteft contact to the mod abfolute confu- 

 fion ; that is to fay, from a mafs of incoherent particles, they 

 become bodies of the moft perfect folidity, and may be found 

 in every fenfible ftage of that progrefs. If they are flightly ce- 

 mented, the ftone is tender and extremely friable ; if much 

 confolidated, the ftone is ftrong, but inflexible, that is to fay, 

 with no more flexibility than the nature of the fubftance and 

 the thinnefs of the body will admit of. It will here be evi- 

 dent, that with the fame degree of cementation or confolidation, 

 and with the fame fubftance, the ftrength of the ftone will de- 

 pend upon the figure of the particles of which it is compofed j 

 the fpherical being that in which the particles are leaft difpofed 

 to be firmly united. But of whatever form the particles may 

 be, or in whatever degree they may be cemented, fo long as 

 their parts, which are in contact, are united, and fo long as 

 thofe particles are rigid, no flexibility, at leaft of that kind 

 which is the fubject of the prefent examination, can take 

 place. 



Thus we may fee, that in order to give any degree of the 

 prefent flexibility, it is neceflary the particles fhould not be all 

 equally united, but be united in fome parts, and difunited in 

 others. By this means, a certain fpecies of articulation may be 

 formed j an articulation which muft be of a complicated na- 

 ture, 



