I 2>4 N A T U R A L H I S T O R Y
projeöion permit that any juice fliould cryftallize in fuch thin,
equal, and continued plates as form thefe fheath s : it’ ia'aJr opihion
attended with much fewer difficulties to think that they all hardened
nearly at one time, and that the whole ffioof-when uniform ja s
produc’d at one effort, but where the ftru&ufe varies, byfomefuc-
cedaneous, dired/ or undulating èffbrts in point of time following
clofe Upon one another; that iff the-lattet cafe' the juices of which
the mafs confifted, gave wdy to the efforts in proportion as their
different mixtures made them more of léfs'ïufceptible b f the motion
impreflèd, the moft agile and pureft ftorie flying off to the greateft
diftance from the center, and the coarfeft and moft°opake remaining
neareft to the center; and to this*flatter opinion I the
more willingly adhere, becaufe (as I hinted before)-tlïefë' ftones’ aiê
generally more dear at the point than at the'‘root, and foëcaufe
in many orbicular lumps of cryftal, particularly Fig.?vii. I find'all
the middle of the lump (,tf, *£,-) opake, terrene, and ‘cloudy;
the fheath next the middle feint and dufky" White,1' the ’next fheath
feint purple; the third a brighter white than' the firft, 'thé' next a
wider feam o f pUrple, but its tinge fainter; the fifth a'imoxe qi-
ftmd white, the next a transparent lift"of'cryftal' in'which the
purple tinge was fcarce difcemable; the laft and outrïiöft df all, thti
pureft cryftal. •« In this fpecimen it is very obferv’abfe' that 'die white
and the purple are alternately fixed in parallel angular fillets, the
cryftal gradually forfekes the purple tinge' as' it" ad Ghees' ’to- the extremity,'
and the white increafes its’ purity ‘iif^thfee 'degrees1 till -it
ends in a fourth of the cleareft cryftal, confirming', (as I fhould
think) what has been hinted before, that the purer- the dyftal, the
farther it proceeds from the center, whilft the moré impure and flug-
gifh parts of die mafs reft ftubborn and unhaoved in thë 'center o f
all. The texture of Fig. xxv. eftablifhes the feme truth; at the
firft effort, the pureft cryftal fled off and coated thd circumference
with hexagonal cufpides; a fainter effort focceeded, whereby the
purer parts of the remaining cryftal were protruded fo from the
center as to form a circle of fubdiaphanous' rays ih ■ the opake
white.
s e c t . x. The variety o f figures in which thefe bodies are found has been
TheMgure. already mentioned, and the caufe to which thefe figures are owing
miift now be taken fome notice of, That thefe ftones have been
in a fluid ftate, and thence paffed into their prefent folidity, muft
evidently appear, by obferving, that the four firft figures, Plate XIII,
page 1 1 g , are of the ftala&ical kind ; that Fig. v, vi, vn, x x i i i ,
xxix, x x x i i i , plainly indicate their having fhot forth as from a
center, protruding themfelyes every way till they terminate in a
point;
O F C O R N W A L L . 133,
point; that Fig. x x v i i is of the .cleareft cryftal inclofing fomething
of. the. mofs .kind, 1 which could never, happen but when the cryftal
was in a fluid ftate. Fig. x x x i is a groupe of hexagonal cryftals
pointed at each end, and immerfed in the fubftance o f one another,
in fuch a manner-as could not. have happened but when fome or
all of them were, in a ftate of fluidity, the hardeft. making their way
into the fofteft, and the fofteft clofely cohering to the hardeft, fo as,
that they both confolidated into one lump. All thefe facts are plain
from, the infpebfion of- .the bodies before us, and there is not the
leaft o.ccafionffo have recourfe (as fome modems have done), to any
jboérpfe chemicgl, anplyfip to proyer? that cryftal, has been, fluid, and
Mpiefofg W^gqenty^is .alfopj^kin, «
tjlat, jdmingiitll? ftate of . fluidity, they, recaved .the feveral figures
ip Ityhicjif'W? m$lY;find them;*,but. to what,'caufe' this .variety ,of
ffigu^es %,pwingjg jpuff be the next enquiry, ,aad is very difficult to
b e /^ fie tj. ■ ■] TtetTil^Qe,, .quatenqs | ftone;?. has not the. faculty of
%vtyuth, fiofficiendy. confirmed, one
would, think, from tbc yaft yfr/tó^pf, quarries, cliffs, and fiffures
offtone in which there is no regular reftilinear form: the ;fhootings
f®f;ftone into fi^ fmall in.pomparifon, few, and rare,, owing
tp) aq^qpt.^and^pii^j^,, pot^the eflêntial produds of the Jirata.
A l f final! quantities, of.lapideous matter would probably form them-
^J.rfCs*.by,lne mutual attraction o f fimilar. parts, and the equal pref-
fluids into .globular maffes,, as water,(-oil, tyuick-
wanÉflfeluid,bodies do» w<§rej4ffnot .for fomething which inter-
thq -ftppy inatjer;; apd prevents this fimple figure from
taking, place. The cryftal which appears in the ftalactical form,;
has nothing, iff itwhich tends to, configuration, more than any common.
ffiapelefs marble, fpar, or killas, and may convince us that
meer. cryftal covets no. particular figure. Cryftal in this ftate wants
that ïaótive principle which throws the feme ftone at other times into
a .great variety of. fhapes; what that principle is, the learned do.
not agijee y but clear it is,. that it is fomething adventitious and
different from cryftal. It has been imagined, that the angularly-
figured I cryftals owe their fhape to the different metals which they
epcoupterv during their fluidity;; but this is.feldom the cafe *, for
cryftals, which are of four, five, or, what is ftill more common fix-
angles, are oftentimes extreamly clear, and have no appearance o f
any,metal in them,- neither do they yield any metal upon trial byfire
that ever I could learn. “ Pure cryftal, and without mixture of
other matter, feys Dr. Woodwardr, concretes ever into an hexagonal
figure, pyramidal or columnar, terminating in an. a p e x b u t we
* See page 147. 5 Cat, vol, I. page 220.
K k have