OF CORNWALL. 109 
if they are interfered by feams of Lone different from the body, 
the reafon poffibly may be this ; that as the body was con trading; 
itfelf in order to induration ( contraction or approximation of parts 
being a neceflary concomitant of induration), or after induration 
cleaved by force of fire or accident, a fiffure enfuing, that fiffure 
was filled with the adjoining matter, repelled by the fubfcance of 
the body, and formed of its own uniform parts by mutual attraction 
betwixt themfelves and exclufion of others. If there are uneven- 
neffes in the furface of pebbles (as was the cafe with many, which 
made Dr. Woodward recur to the agitation of the waters of the 
deluge) fome parts being more prominent than others, or if there 
are loofe nucleus’s incloled within the central cavity, as is the cale 
of the fEtites ", it need only be fuggefted, that thefe phasnomina 
may reafonably be attributed to the different contraCtile powers of 
the materials ol which thefe unevenneffes and central nucleus’s con- 
lift ; it being certain, that if the body of a ftone contracts itfelf, 
in order to induration, into a clofer fubftance than the feam, feptum, 
or granulated charge , that charge or feam will be more prominent 
than the body, and vice verfd ; and if the fubftance of the nucleus, 
during the time of induration, contracts itfelf after and more than 
the fubftance of the fhell which invefts it, that nucleus will have a 
vacancy round it, and become loofe in its cell, the nucleus being a 
concretion pofteriour to that of the fhell, and breaking loofe from 
the inner coat of the fhell by the contractile powers of its own 
conftituent parts. Laltly, of pebbles : Some are evidently formed 
fince the deluge, for we find fhells, coralloid bodies, and echinites 
in them ; whether thofe which carry no fuch evidences were formed 
before, at, or long fince the deluge, it is impoluble to determine. 
From pebbles, let us pafs to nodules of curious ftones found in sect.iv. 
Cornwall. Having found fome pebbles of porphyry on the fea- Nodules, 
ihore, upon farther fearch I difcovered a ftone of the fame kind 
in the parifh of Philac, among the fand-hills : it is of a ruddy- 
purple ground (not fo red as the Egyptian) charged with granules 
rectangular and oval, from the eighth of an inch diameter and under, 
nearly of the fame colour with the ground , but paler with glofly 
furfaces, interfperfed thinly with opake white granules of quartz of 
like fize and fhape to the foregoing, mixed with fome black Ipecks of 
cockle of the fame fize. It weighs to water as 2 - - 7ft to 1 *. 
N°. ii. Part of a large nodule of like porphyry found in my 
garden, had its granules larger, but no white interfperfed. One 
z One of which, of a hard brown flint-like and brought me September 17, 1757- 
ftone, about an inch in diameter, was found in a This feems to be the pophyrites leucoftidttos 
*757, near Penzance Kaye, among the fea-pebbles, of the ancients. 
F f pebble 
