C 61 ] 
' diffufed throughout the whole globe, and mixed in 
fome degree with moft ftratas. Thefe fmall particles, 
I apprehend, are carried along gradually, by the 
moifture, or vapors, which foak through the pores, 
till they come to Tome cavity, and there, being flopped 
by the difcontinuance of the earthy or ftony fubflance 
from proceeding any further, they collect together 
in drops, and as they dry and harden, do of coui fe, by 
their mutual attraction, form themfelves into cryftal- 
line figures ; and as the pores are more and more 
filled up, by the acceffion of more corpufcles, or by 
their mutual attradion which draws them clofer 
together, they become more and more tranfparent. 
Some, however, of the bodies thus formed never have 
any tranfparency at all, being mixed with too many 
earthy or ftony particles, or other heterogeneous 
matter, and have fometimes fo much of that as not to 
be able to put on any regular form, but only to petrify ^ 
in a confufed heap ; the earthy or ftony particles pre- 
venting the cryftalline or faline particles fiom forming 
themfelves, by their mutual attraction, into regular 
figures j and there being perhaps but few of the true 
cryftalline corpufcles mixed with them. This feems 
to be the cafe with many of the ftony concretions in 
large caverns : and perhaps, from a fmall mixture of 
thefe fame heterogeneous particles it is, that fpars are 
inferior to cryftals, and alfo differ from one another. 
Mr. Platt, in the Philofophical Tranfadions, Vol.LIV. 
p. 41. has obferved, that fpar feems to be nothing but 
cryftal debafed by a calcareous earth. 
I cannot help fufpeding, that what I have called 
cryftalline corpufcles are in reality a kind of falts ; I 
will beg leave, therefore, to call them hereafter by 
D that 
