DISTRIBUTION OP METALLIC VEINS AND MINERAL BEDS, &C. 47 
ally from the tin and copper mines of Cornwall, of the 
dependence of veins in regard to their productiveness, and the 
kind of ore they yield, upon the character of the including rock. 
The formation of veins must evidently have been less sudden, 
tumultuous, and mechanical than it has been represented. Neither 
simple solution nor simple fusion, with subsequent precipitation 
or crystallization, will account for the appearances. Nor is sub- 
limation from an interior source of heat, which has also been 
proposed as the cause by which they may have been produced, 
less liable to objection. None of these hypotheses account for the 
influence of the including rock, upon the richness and other char- 
acters of the vein by which it is traversed. 
When we look through nature for an agent, competent to the 
production of the effects we are considering, that whose modes of 
operation and the laws by which they are regulated, are the ob- 
jects of the science of Galvanism, presents itself as having the 
best claim to a fulfilment of the required conditions. It is now 
but fifty years since its existence was first suspected, and our 
knowledge of its powers is still limited. It has been ascertained, 
however, that matter is transferred by it from one point of space 
to another, without any clear indications at the time, of the changes 
that are going on, and that subjected to its influence, one chemi- 
cal element is made to traverse another for which it has a strong 
affinity, without any combination. It is also excited and brought 
into action by the application to each other, of surfaces of different 
nature and constitution, such as the strata that constitute the crust 
of the earth are — and according as these differed from each other 
in composition or magnitude, it was to be expected that the ac- 
cumulations would be directed on some points in preference to 
others. If galvanic electricity be the agent by Which veins have 
been formed, we may refer to it all the different kinds, whether 
earthy, metalliferous, contemporaneous, or of date subsequent to 
that of the rocks in which they lie. 
DISTRIBUTION OF METALLIC VEINS AND MINERAL 
BEDS THROUGH THE STRATA.. 
28. Is the distribution of metallic veins and of valuable minerals 
of every kind through the strata of the globe, regulated by any 
general laws, or is every kind of ore or other fossil found indis- 
criminately in every formation from the oldest to the most re- 
cent? Some statements in relation to this subject were intro- 
duced into our account of the rocks, which it may be useful to 
recapitulate in connection with a few additional remarks in this 
place. 
1. Metallic veins are confined to the primitive, transition, and 
the lowest, or most ancient of the secondary rocks. The cause, 
whatever it was, which operated in their production, had ceased 
