i2 8 natural history 
lapidific matter (when drained of fuperfluous moifture, and difpofed 
to fhoot) happens to be, fo will the tendency of the fhoots, both 
column and point, be : in all concave beds, lor instance, tne points 
will converge ; in all convex ones, they will turn the contiary May . 
if the concave part, for example, of the ammonites, Fig. XXXII J . 
be fet with cryftals, their points will tend inwards towards the cen- 
tre, being thereto compelled by the regular contour of the cornu- 
ammonis ; but if the cryftal rifes from a convex bed, or orbicular 
lump, then will the columns fpring as from one common centre, and 
point forth their radii , as in Fig. XXXI II* PI* XIII. p. 119. If theie 
be a thin plate of cryftal, equally expofed to the influence of heat 
or cold on each fide, with equal room and force to fhoot, it will 
throw forth its points on each furface, and the line, from which 
the fibres began to fpring, fhall be exactly in the middle or fuch 
plate of cryftal, as Fig. v. Fig. vi, ib, is alfo eafily to be accounted 
for on the fame principles : it is the fection of an oval lump of 
cryftal, equally impregnated with fait ; it muft therefore fhoot as 
from a line or commiflure in the middle ; for the contiguous co- 
lumns, being protruded on every fide with equal force, muft be of 
equal length ; if the lump had been globular, thefe rude columns 
would have fhot as from a center, as in Fig 3 , xxill. and XXV. ib. 
the fibres do. Hence I conclude, that the direction of columnar 
cryftals is nearly rectangular to the plane of the bed from which 
they iflue, and that all the feeming confufion in the pointings of 
thefe bodies in the mine above-mentioned was owing to the great 
variety of furfaces and angles into which that large body of cryftal 
was hardening when thefe hexagonal cryftals fhot from its extremities. 
CHAP. XII. 
Of Semimetals found in Cornwall . 
F ROM ftones of ornament and curiofity come we next to the 
products of the mines and ftones of profit, few countries, 
according to the judgment of foreigners, exceeding this county in 
the variety and plenty of minerals z : but we have rather the pof- 
feffion than the enjoyment of this treafure ; for though this multi- 
tude and variety appears every where in thofe parts moft fubject to 
mines (I mean from St. Auftel weftwards), yet few of our people 
y From Mr. Allen’s quarries at Bath, none of alphabeti fui mineralis fe credere nullum terrarum 
that fort being yet difcovered in Cornwall. locum reperiri qui minerarum multitudine et vari- 
8 Beecherus rcfert de Cornubia in dedications etate antecellat. 
(erigrofled 
