166 NATURAL HISTORY 
or the earth and fubftance of the lode is fo porous, that all the 
nourifhment of the manure is diflipated, and finks below, inffcead 
of being raifed into the plants. 
Much furer indications of treafure are often found in cliffs and 
caverns, where the lodes, being laid bare for fome fathoms in depth, 
may eafily be examined at its feveral ftages. 
Some of the curious will think that difcoveries may be made by 
obferving the pofition and alteration of the feveral Jlrata as we 
defcend in our mines ; but there is no fort of uniformity to be af- 
fumed in the Jlrata of one hill and thofe of another half a mile off, 
no relation betwixt the lodes and Jlrata , as to depth, width, feeder, 
length, colour, or texture, and therefore no judgment can be formed 
from the lituation of the Jlrata in one place, where, how, or in 
what condition lodes are to be found in another place ° . 
In order to make difcoveries, fome drive adits p or drifts through 
their grounds, but few can prevail on any fellow-adventurers to 
bear fo heavy an ex pence where the fuccefs is fo precarious. It is 
much ealier, and lefs expenfive, and therefore moft common to trace 
lodes by the fcattered fragments of them called fhodes (fee pag. 149. 
feet, iv.) ; and as this is a kind of fcience which few tinners under- 
ftand but thofe who have chiefly applied themfelves to thefe refearches, 
it will require more particular notice. If the fhode is found in the 
vegetable foil, it gives no evidence of any lode’s being nigh ; but if 
in the fajl , (that is, the rubble or clay never moved flnee the flood) 
it is taken as a never-failing proof that it came from a lode farther 
up in the hill. As foon as the fhode is found impregnated with 
tin, to find the lode it came from is the next care ; the procefs 
confifts in digging pits at a proper diftance, depth, and in proper 
direction, and judicioufly regulating their advances to the lode ac- 
cording as the properties of the fhodes diretft. Firft, the run of 
the lode being known to be in the hill above the fhode, the feveral 
declivities below the hill, and where water may be fuppofed to have 
run with greateft force, muft be confidered, and there, at right 
angles to fuch force, muft; the fhafts 11 be placed crofting fuch decli- 
vities. For inftance, let A B, Plate XVII. Fig. vii. page 149, be 
the feeftion of a hill in which there is a lode running eaft and weft 
at C ; D is the broil or loofe capping of the lode ; S S the outward 
coat or furface of the ground ; the fhodes proceeding from the lode 
C D, fhall be found courfing down the declivity of the hill in the 
dire&ion of G H. Again, Fig. vm. Plate ibid, gives us the ich- 
0 Something however of fuch recitals may he 
feen collected by Dr. Woodward, Cat. vol. I. 
page 201, &c. 
p Subterraneous paffages for the water to run 
off, and for better communication betwixt the fe- 
veral parts of the mine. 
'i Called, in the Cornifh tongue, Cofteaning- 
Ihafts, fromCothas-Stean, i. e. fallen ordroptTin. 
nography 
