VOL. LVir.] PHILOSOPHICAL TRANSACTIONS. 385 



comes transparent by being oiled, and the oculus miindi stone by being soaked 

 in water. 



These are the principal observations on which Mr. K. founds his conjectures ; 

 and hence he is induced to conclude, that all these above-mentioned substances, 

 are formed by means of those crystalline, perhaps saline, corpuscles, with which 

 the surrounding earth or porous stones abound, and which probably are diftUsed 

 throughout the whole globe, and mixed in some degree with most strata. These 

 small particles, he apprehends, are carried along gradually, by the moisture, or 

 vapors, which soak through the pores, till they come to some cavity, and there, 

 being stopped by the discontinuance of the earthy or stony substance from pro- 

 ceeding any farther, they collect together in drops, and as they dry and harden, 

 do of course, by their mutual attraction, form themselves into crystalline figures ; 

 and as the pores are more and more filled up, by the accession of more cor- 

 puscles, or by their mutual attraction which draws them closer together, they be- 

 come more and more transparent. Some of the bodies however thus formed 

 never have any transparency at all, being mixed with too many earthy or stony 

 particles, or other heterogeneous matter, and have sometimes so much of that 

 as not to be able to put on any regular form, but only to petrify in a confused 

 heap ; the earthy or stony particles preventing the crystalline or saline particles 

 from forming themselves, by their mutual attraction, into regular figures ; and 

 there being perhaps but few of the true crystalline corpuscles mixed with them. 

 This seems to be the case with many of the stony concretions in large caverns : 

 and perhaps, from a small mixture of these same heterogeneous particles it is, 

 that spars are inferior to crystals, and also differ from one another. Mr. Piatt, in 

 the Philos. Trans., Vol. 54, has observed, that spar seems to be nothing but 

 crystal debased by a calcarious earth. 



Mr. K. suspects, that what he has called crystalline corpuscles, are in reality a 

 kind of salts ; he therefore calls them hereafter by that name ; and now en- 

 deavours to illustrate what he has said more particularly by the instance of Bristol 

 stones. In their first state, these are of a dirty red, or some other dusky colour; 

 but afterwards, as more salts, or crystalline corpuscles, are added, by the descent 

 of moisture, or the passage of more vapour, they begin to be more compact ; 

 and then, the pores becoming smaller, they approach nearer to transparency, 

 and put on a yellow or whitish colour ; and at last, receiving a further addition of 

 salts, and having the component particles drawn still closer together by their mu- 

 tual attraction, they become still harder and more transparent, till they acquire, 

 by a lengtli of years, their greatest degree of perfection. 



In such formations he considers the largest caverns in the earth, and the 

 smallest cavities in stone, as producing similar effects, and therefore considers 

 them in the same light : for wherever there are cavities in the earth, or in stonesi, 



VOL. XII. 3 D 



