OF CORNWALL. I45 
of running waters. The largeft fiffures which we are apt to wonder 
at, extending themfeves in one direction for fo many miles, are no 
more to the body of the earth than the fmalleft, and to the naked 
eye invifible clefts in bricks, ftones, and minerals ; they are but lo 
many terminations of the effort, whereby fimilar, foft, and moift 
bodies contradcd themfelves, and paffed into drought and hardnefs. 
I need not fay, that, according to this theory, the paflage of the 
waters through thofe clefts was the confequence and effed and not 
the caufe of thefe fiffures, as Agricola fuppofed. Which is moft 
likely, muft be fubmitted to the candid reader ; but the above ac- 
count feems to be confirmed from a very common and juft obfer- 
vation, that where the failures are wideft, there they are feweft ; 
and, on the odier hand, proportionably fmall where they are moft 
fi equcnt ; boih equai evidences, that the concreting glebes could 
not harden without cracking to a certain degree; that, where a large 
chink enfued, it anfwered all the exigencies of the contrading-mafs ; 
but where the ci cvicc or eafement to the forming-mafs was but 
fmall, there many cracks did fupply the place of a large one. 
That the breadth, depth, and length of thefe fiffures are all dif-SECT. iv. 
ferent, fliev/s that they are not the effeds of any exact rule, but Properties, 
the product of feme natural immechanical operation, on a various, 
mixed, and unfettled congeries of bodies concurring to form them- 
iehes in different fhapes, quantities, and pofttions. 
iiwm feems to be fome uniformity in the diredion of our Cor- Direction, 
nifh fiffures, pointing, as they generally do, eaft and weft. In the 
coal and lead-mines throughout England, they generally do the fame 
as Mr. Ray obferves (Phyficotheol. page 378); but, from fuch 
fmall fpots, nothing certain can be concluded; and there are fo 
many fiffures in contrary and more oblique diredions, that no uni- 
formity in general can be prefumed. The four principal veins of 
Poton run north and iouth, and thofe of Oruro, reckoned the fecond 
beft in Peru, have the fame courfe, though on a different fide of 
the mountain. At Schemnitz, in Hungary, the veins of filver-ore 
run north and fouth, other rich veins north-eaft ; all veins keep not 
to the fame point, even in the fame mine.” Brown’s Travels, pa. 
57 * Of the gold-mines, in Schemnitz, fome run to the north, 
fome to the eaft, ibid, page 63. In the mines of Gottenberg, in 
Bohemia, the veins of filver and copper run fouth, ib. page 162. 
That the north and fouth fiffures fhould be generally fmaller than Magnitude, 
the eaft and weft ones, is merely accidental ; for they are fome- 
times as large, and larger. In general, we may conclude, that the 
fiffures were large or fmall in proportion to the adivity of the con- 
fading maffes on either fide. Again, as the forces of that con- 
P p tradion, 
