120 NATURAL HISTORY 
formation of them in the ftala&ical manner can admit of no difpute. 
They are of the colour of fine glew, tranfparent as gum-arabic, and 
to the eye of like texture ; they end in one drop as round as any 
drop of dew or rain whilffc it hangs ready to fall. It breaks like 
flint into irregular, edgy Iplinters. In Fig. iv. one of the ftalac- 
tical productions, <3, was evidently wreathed and twilled from the 
ufual perpendicularity, by fome force (in the mine) either of fire, wind, 
or water. This mult have happened whilft as yet it remained in its 
liquefcent tender ftate ; but the liquid was lo ftiff and clammy, that 
though the three pendant procefles were connected by this force, yet 
the circumference of each procefs, its annular tumours, and the termi- 
ing drop of each ftalaCtite, is plainly to be difcerned. Among 
the plain-cryftals I lhall alfo reckon the pebble-cryftal ra ; for this 
feems to owe its orbicular figure to nothing more than what is com- 
mon to all bodies, I mean, the gravitation and mutual attraction 
of fimilar parts aflifted or controuled by the medium in which thefe 
round mafles formed. Cryftal, in all thele circumltances, has no 
uniformity of figure, gives no evidence of any inherent aCtive prin- 
ciple, but fuffers itfelf to be falhioned and molded by its own gra- 
vitation, by the nidus it refts in, or by the medium which furrounds 
it, and yet is perfect cryftal, breaks irregularly, gives fire plentifully 
with fteel, is very hard to the graver, and ferments not in the leaft 
with aqua forth. 
sect. iv. But though the Cornifh cryftals in thefe inftances are pafiive, 
cryibif an d covet no particular figure, yet, in a great variety of inftances, 
they are figured either uniformly, or with fome accidental differences. 
Cryftals are moft generally found in the hexagonal form, and in 
thefe three different ftates ; either pyramidal, as Fig. ix. Plate XIII. 
their fix fides tending to a point ; or columnar, the fhaft capped 
with a pyramid, Fig. x. ib. ; or columnar with a pyramid at each 
end, as Fig. xi. ib. (page 119); making in all eighteen fides or 
planes. 
The fides of the fame mafs are feldorn of an equal breadth and 
length, fome fides being more than three times as wide as others, 
as in Fig. vm. and xv. ib. neither do they always end in a fharp 
point; fometimes the point is fhortend and notched, as in Fig. xm. 
ib. each plane of the cufpis making a diftinCt angle. 
Sometimes the point ends in a fharp edge, as Fig. xii. xiv. 
vxii. 
The pyramidal cufpis is not always hexagonal, but fometimes 
tetragonal, confifting of four equal planes, as Fig. xii. ending in 
* Before page, 104. 
an 
