TAB. CCVITII, 
SILEX Quartzum. 
Laminated Quartz. 
Div. 1. Crystallized. 
EE 
Tuer more we become acquainted with Mineralogy, the 
more we have to admire. 
The nuclei of crystallization often form in plates ; but, 
in the present instance, it should seem that, by some in- 
terruption of a particular nature in the dissolving men- 
struum, the crystal could not be formed so smoothly and 
regularly as is common with crystallizing Quartz, and ¢ab. 
i99 shows that it may be mixed with much foreign matter 
without altering the regularity of the crystallization. Thus 
the present subject is the more remarkable. This sort of 
Quartz has been found pretty frequently at Glassteining, in 
Cornwall, but I do not know that it has been found else- 
where. It has often Tin and decomposing Felspar about 
it; and whether these or any other decomposable substances 
have been originally formed with it, and have since caused 
its decomposition, as seems to be partly the case with the 
Pebbles at tab. 103, either way it is a curious circumstance, 
and may lead to some useful truth in the investigation of the 
