152 N A T U R A L H I S T O R Y
its contents. The lode is either barren or impregnated. Many of our Ibdes
in Cornwall are happily flocked with plenty of metals, but-the
richeft are not equally inapregnatedin all parts, and ' numbers tof
lodes have nothing metallic in them: there is nothing 1 conftantly
uniform in the bowels of the earth ; metals are not more differently
diftributed among climates and countries than they are oftentimes
difpofed in different parts of the fame mine. Hence arifes great
uncertainty and frequent lofs in mining, the'certain gain, even here
in Cornwall, where metals are in fuch plenty, being only the maintenance
and conftant employment of the labourers and artificers
depending on the mines, and the confumption of materials which
bring in a considerable revenue to the publick whether the adventurers
gain or lofe.
The lode is not lb often two feet wide and more, as it is one foot
and under; fometimes however it is wider, but, generally fpeak-
ing, the fmaller the lode the better impregnatedc.
Lodes either confift o f hard, Iblid ftone, or are lefs compa&j.foft,
and crumbly. I f the adjoiningy?r«ra have yieldedpferitiy- Jff||li<||iid
fpar and cryftal to incruft the metallic particles, then the tin or .other
metal is found inclofed in (olid, hard, ftony fufiftance $ hut where
nature has been more fparing of her cement, the . ore i^ .found ip a
lax, arenaceous, and rubbly ftate: both hard and. foft lpdes ; may
be well and equally impregnated, but loft lodes are more apt to
have their metals difperfed.
s e c t , v i Lodes are leldom perpendicular ; they decline as .they defcend,
Ttelndj- either to the right hand or to the left, but in vety different degrees;
S ta e of and the lame lode may decline in one part to one fide of the per-
pendicular, and in another part to the oppofite fide. This declination
increafes as it approaches the fides of hills, and the cliffs of
the fea-£hore, of vallies and of rivers; but the lame lode which
Ihelves away quick at the declivity of a hill, or the approach of a
precipice, when it gets upon a champaign plain ground, coafts it
almoft upright. Again: Lodes are not only inclined but fradtured,
and the inclined fragments found leparated from each other by the
intervention of earth ftone, or both, entirely different from the
lode; from whence it follows, firft, that fuch lodes were formed before
the fradure; fecondly, that as the fradure muft have been the
effed of violence, and probably of a violent agitation, the inclination
muft have been alfo the effed of force, although in many inftances
that force only bent, and did not proceed to that degree of violence
as to occafion a difrupture of the lode; thirdly, the firft diredion
* In the parifh of St. Juft (Penwith) the lodes are feldom wide, but the tin is of the beft kind.
of
C O R N W A L L . '• 1 53
o f the lode was the perpendicular, or nearly fo, and the inclination
and fradures are but two different degrees of variation from it. If
therefore we can difeover the probable caufe of the inclination of lodes,
the fame caufe, allowing it but a greater impetus, will account for
the fradure. Now betwixt the inclination of lodes, and the dippings
of the. adjoining. Jkata<v .there, is oftentimes(tho’ not always) To ma-
nifeft ^ . agfpe^inn an^, correlpon^enipev that whatever occafioned
the. latter could(not but produce the former. Let;u^ firft note the
dippings of th e ^ r a fa J ot if they frppe alfo been wrefte;d, the
lodes contained t*in them pquld not.j ha^greferveef their ftation. As
| | ^ r i g ^ :;pqfit§bfr;^^ o f the. jitrpta
each ftone,, Jartfo land,. gravel; ^ndTheir
commixtures, refting (for the moft part} according to their differ-
and ^Ippeading in belts andj floors nearly parallel to
the furface oTtodjqarth; ,but we, often find thefe J ra p . Very fenfibly
declined from that, £heir firft pofition;, nay fometimes quite reverfed,
and ' changed info ^perpendicular. ;^Thus, , forsiinftance1 the, rocks
and ledges on each frde of. large rivers,;’ laid bare by .tides, are frequently
.obferved to turn their points, and thin edges down towards
the.,chanel, intimating, that, from horizontal,'
forw^d towards each other, making an angle in the middle, in
which the waters pals, as in Plate X\fil. Fig.: i page 149. A ^ in :
In finking on the ndes arid bottom o f vallies, we. find die natural
Igiek or karn, G, H, F. ibid.) equally covered with earth
and rubble, and rumrin g, nearly in a plane parallel to/the furface of
‘the ground. ( For .inftance, at^ the, hill, E, the karn fhall be ten
feet under the furface; in the bottom C, it fhall be fomewhat
deeper, that is, more covered hy what is wafhed off from the fides;
and as it coafts upwards again to the Kill D, it fhall be buried only
ten feet again, as at F. Now the lode which erodes fuch vallies,
rifes and falls, as the karn G, M, H, which cannot therefore be the
natural firft fite either of karn or lode; for it is utterly impoflible,
that any fiffure, being an open chanel, could contain in its fides
M, L, K, any liquid (which all lodes muft at firft have been) if
they were formed in fuch a curve^line; as much as that a fyphon, if
the tube was flit and open on one fide, fhould draw water: this
obfervation therefore will lead us to this further truth, that the fub-
fidence of fuch vallies muff have happened fince the formation of
lodes, and that the Jirata, in many inftances, have departed from
their primary pofition; which was to be fhewn. But the Jirata have
not only dipped in feme places lefs, in iome more, but from horizontal
have become perpendicular. Now, when we fee a wall
lean, we conclude immediately that the foundation has given way
according to the angle which the wall makes with the horizon; and
R r " when