244 On Mineral Veins. 
as to render it profitable to quarry and crush the surface 
rock in many places. 
The stream tin of this colony, and most of the gold asso- 
ciated with it, appear to have been derived from the decom- 
position of the oranites in the neighbourhood of which they 
are found. ; 
The obstacles enumerated have been felt even by the 
staunchest supporters of the above theories; and it has been 
suggested that deposition from sublimation, from currents, 
and from the bounding rocks, may have been going on at 
the same time. It is not probable, however, that nature is 
working by several distinct means in filling the veins ; and 
if it is found that the theory of deposition or aggregation — 
from the bounding rocks will account for all the phenomena 
observed, and as it is the only theory which will do so, it 
may be safely accepted as the correct explanation of the 
mode in which ores have been deposited. 
No doubt, in localities where powerful volcanic action is 
going on, metallic ores may be deposited from sublimation 
in sufficient quantity to afford cabinet specimens. And the 
veins acting as channels for water holding minerals in solu- 
tion an occasional deposit may occur in this way, or a trans- 
fer of the ore from one part of the vein to another, or even 
to joints. or veins adjoining it, may be effected. But a close 
examination of all the phenomena attending the deposits in 
veins leads irresistibly to the conclusion that the great bulk 
of the metallic ores have been derived from the bounding 
rocks. 
In the experiment carried out by Mr. Hunt metallic copper 
and carbonates of copper and zinc were deposited along the 
curved laminations in the clay wall, forming in fact an 
artificial mineral vein. In the same way Mr. Fox obtained 
deposits of peroxide of tin and other ores, and proved that 
long-continued electro-chemical action with weak currents — 
is able to overcome strong affinities, decomposing some — 
bodies, and forming new combinations. Using the same ~ 
agents, Becquerel has produced crystals of the sulphides of ~ 
tin, copper, lead, and iron, and oxides of copper and zinc; ~ 
and there can be no reason why the same minerals should — 
not be produced by the same agents in the laboratory of — 
nature as well as in that of the chemist. 
In nature will be found all the requisite conditions 
operating ona grand scale. Magnetic currents traverse the 
rocks capable of exciting the necessary action, and bearing 
