92, ;A-^T~U R A L H^l S;rT l'0 R Y
nature' -léfi>it in ; it' iè, not - found&ih llratö* or quarries-but; in 'de-
tachéd-angïïlkr malfe,; fometimes in large .rocks',1 and "is' ufkally^óf
a'l^ey' bliierfli colöüf. - If the nodules of ‘tills dtbne'- are found of' a*
'porfoble^fizfe1 and a plane fü-pfaee, fo ak to need?little pplifoing,t-'ühey>
make ftorieS -for grinding the moft,-precSoüs colours, far bfeyond;any
marble and 'ö|Uil‘to* any porphyry., 1 -
i -; There- is; another fort of Elvan, which Gonfifts of a yêllöW- oljSy*
cement,' thick fet with opaque, white and yejlow ;cty ftalline gra-;
miles, and- thdfe 'thinly belprinkled with cin'ereóus grairiS"jpSë|^
-the grains and - granules have fmooth and-; plane .foffaéës-^ 'This;
Rpne rife in a quarry at Boreppa in Camborn,' and ekfewhprey’is,. found!
m large nbdülesj immeried five, feet deep and: more in StenVïdrlak
clay-pits: inLudgvan, and in imoothed nodufe ön thé'-beach betwixt
Penzance andMarazion j it is not near:fo hard as .the: femme».:
s e c t . iv. More common - flail, of more various appearance and necèflaiy
Kate* ufe; is the ffone whidH we call Rillas *. It" ïskof :f(hëichifrosd£ixi,d,-
fome doits more, friable,^ and: fome, more laminated th&iri&e reftï?-
•there is icarce any field or common, where in fome1 lhape:ror othéi*
we do not find thefe Hones, huttwhefe there" are ;ahy quarriesi of
-it, the top of the ftratum is covered -with - loofe, thiirftohesd inter-
Iperfed with earth and clay, ahd'ajfew^lèet below, Hes thefc^dfi0®6*
-the crevices of which are nearly, perpendicular, .and horiimföli; .thefo
ïfones generally dip towards the Weft, .andb rile, .flat, ofla?.^fery .even
thickriels, for which reafon I imagine they iaïe-Sllcdjhy.the. Tinners;
-Raze b ; Bave^-a finooth 'face*,:for .building, dirdi/rnake a
llrong wall, but are apt to bg tfeathcr^edged,^:which makes ;thehaL
lodge water, and throw damps into the walls. There* are thre^
forts of this ftone, the yellow, ;the,cinereqO’s 'O^bhaeifliy' and’ thé
brown The yellow is hard and tailing, if laid in jnèaSly; the lamb
. figure as it rife, but breaks eafily.into lhivérs,:.aOd aerp(^the;grairt,
lb that it will not bear hammering;; it does,.n0tfermerit.vifijthr%^»
fortisy npr give fire with Heel, o f a laridy grit and uniform texture,
with a yellow ochreous clay in it’s comnaiflbres, • and. weighs tp
water as 2^ is to one.
The blueilh killas is fometimes lb exceeding hard and ftubborn,
that in the,mine they give five pounds a fathom 'for breaking it ;
at Other times it is as eafy to break as pitcoal.. Round the town
of Marazion, and other places, (but better Hill ■ in = a large and
ancient quarry at Hellion in Kerrier,) there riles, a very... fendef
killas, of ,the. cinereous, and alfo of the yellow .colour,. both
Iprigged with lpecks of a darker hue, the texture of both the lame,
* P r* Woodward Cat. V . ii. pag. 6. fays we call * Woodward’s Cat. vól. i* ,pag. 2ÓH tn. 9» .
any ftone killas that fplits with a grain, f Six feet long, fix high, and three wide.
viz;
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