466 Royal Institution. 
water impregnated with metallic salts, the sterility of cers 
tain spots of land, the frequent appearance of light in par- 
ticular places—an electrical phenomenon, probably, owing 
to the great conducting power of metallic ores, &c. guide 
the miner in his search. Metallic veins are sometimes dis- 
covered by means of the fragments separated from their sur- 
face: the tracing of these scattered fragments to their ori- 
gin is in Cornwall called shodeing. The divining rod, 
which is a forked hazel twig, was formerly in great repute 
for discovering metallic veins and springs of water. The 
rod itself can only be influenced by the hand holding it ; 
and as metallic veins and moist strata are superior conductors 
of electricity, a slight electrical effect consequently may be 
produced on persons possessed cf great sensibility, in their 
neighbourhood. But the effect is so vague, that it affords 
no useful or certain indication. And itis a vulgar mistake, 
that water is confined to any particular part of a stratum ; i¢ 
is usually diffused through the sand, gravel, and clay com- 
posing it, and will collect wherever pits are made for its 
reception. 
The direction of veins,, thouch their dispositions and ra- 
mifieations are very irregular, 1s generally uniform, The 
direction of metallic veins is, with Jittle deviation, from 
east to west. Veins the course. of which is from north 
to south are seldom metalliferous, .. These, veins pass un- 
interrupted through the preceding, sometimes. merely cut- 
ung their line of direction, at others removing laterally one 
part of the divided vein to some. distance Asasthe other. 
-The derangement, thus produced is a pad | called. the 
heave of the lode dr veinm--Crosg veins of hasalt are curi~ 
ous, On account of the horizontal, position of. the pillars 
into which they are commonly'split;.....,,...4.., |. 
Basaltic veins, are of the latest formations : consequently, 
as they intersect and derange, natalie jveins,. it necessarily 
follows that at present there 4s;ho, production or renovation 
of ores, and that aka eed idea, that the exhausted: 
parts of mines are -repler ished,. is erroneous. Mr. Davy 
noticed the hypothesis Oe Bechet eieabel and Lehman, 
respecting metallic veinsy founded-on this notion. 
Metallic veins, like the secondary rocks, are the produc- 
tion of an ancient and obscure period, when the ocean 
overspread the surface of the present land. And _ before 
the mysterious subject of their formiation can be understood, 
there must be a great extension of chemical discovery, as 
well as a collection of geological facts. 
Lecture V.—In this lecture Mr. Davy considered the 
causes 
