Dr. Eafon on Cryftallization. 35 
tion by the concentrated rays of the fun; and, 
perhaps, there are, or have been, degrees of 
heat in nature, fufficient to produce the fame 
effect. Is it not poffible, that thofe immenfe 
fires, which feem to be the caufe of earthquakes 
and burning mountains, are fufficiently ftrong 
to bring into fufion the pureft kind of verifiable 
earth ? Is it not probable, that from fufions 
thus effected the whole tribe of precious Hones 
have been formed by cryftallization ?* 
If this conjefture has any foundation in nature, 
it will enable us to account in a very fatisfadtory 
manner for all the peculiar properties obfervable 
in this clafs of bodies. If the melted matter, in 
which the vitrifiable earth is diffufed, be fuffici¬ 
ently fluid, and if the cryftallization be carried 
on with due regularity, the cryftals will be well 
formed, and will exclude from their compofition 
all heterogeneous matters. If, however, the 
melted matter be too tenacious, or, if the procefs 
be carried on with too much rapidity, the cryftals 
will be irregular, and involve in their compofition 
more or lefs heterogeneous matters, according to 
* The difficulty of accounting for the fufion of the 
earth, conftituting the precious Hones, is obviated by the 
experiments of the celebrated Bergman, whofe analylis of 
thefe fubflances had not been feen by the author, at the 
time of writing this paper. For, from thefe it appears, 
that the gems'contain not only vitrifiable, but argillaceous 
and calcareous earth. 
D a 
circum- 
