( 4®5 )• 
hexagonal Fyr amid. Where this plaftick Power hap- 
pens to be (ingle and uncontroul’d, itpreferves the Form 
of the Criftal to very conliderable Magnitudes. 
In thefe (ingle Criftals we may obferve, that they are 
of different Tranfparencies and Colours, as the (tony 
Matter is more or iefs difengaged from other Subftan- 
ces ,or as thofe other Subftances are capable of impart- 
ing different Tinctures to them. And that they feem 
form’d laminatim \ tho’ the Lamina are only diftin- 
guifhable, when the Matters from whence the Criftal 
is fucceilively form’d, happens to differ in Purity. 
Thus in Figure the fourth , the Criftal was at firfl 
form’d from Matter intangled with a foul yellow 
Subftance^ after which, a pure Matter advening, the 
Criftal was in its future Lamination form’d more pure 
and tranfparent. 
But where the plaftick Particles are more numerous, 
there feems Reafon to believe, that thefe very Flaftick 
F articles, before they are fix’d, are fubjed to the 
Controul and Direction of any fix’d plaftick F article, 
within the Verge of whofe Adivity they happen to 
move: notwithftanding which, after they are once 
fix’d, they exert their own plaftick Fowers , and, in 
Conjundion with the firft plaftick Farticle , govern 
the future Concretion, in luch Manner as to form a 
feemingly irregular Criftal, tho’ compofed of two or 
more regular Criftals. Thus in Figure the fifth and 
fixth A and C feem to have attraded amongft the ftony 
Particles, two plaftick Particles, which afterwards ex- 
erting their own Powers, form the additional Criftals B 
and D. 
There are many Phenomena obfervable in thefe 
Criftals, which, at prefent, 1 may pafs over, as lefs re- 
lating 
