88 Of th FLEXIBILITY of 
articulation, while it preferves the component particles in one 
entire mafs, fuffers the parts to move a certain fpace in relation 
to each other. 
Bur before diffe€ting this ftone, in order to fee upon 
what principle it holds its flexibility, it may be proper to form 
a diftiné 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 {trata are 
thus aétually found, with their particles united in every poflible 
degree, from the flighteft conta& to the moft 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 ; 
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 
. . re . ~~ 
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 fubje€t of the prefent examination, can take 
place. 
Tuus 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 ; an articulation which muft be of a complicated na- 
ture, 
we * 
