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ae 
Quartz and Metalliferous Veins. 345 
it must, therefore, be considered as a necessary conse- 
quence, that if ever fused silica had been injected into a vein 
fissure in clay-slate, there would have been formed, after 
the gradual cooling and consolidation, not a vein of pure 
quartz, but a crystalline vein stuff, of the nature of granite, 
in as far as the adjacent rock could have furnished the ne- 
cessary bases for the production of granite. If, therefore, 
we could suppose that ever pure quartz in fusion rose up 
from beneath, we might also, on the other hand, conclude, 
that a granite vein, in a country of clay-slate, would be pro- 
duced ; but not that a quartz vein could have been formed 
in such a manner. 
To these difficulties of conceiving the rising of fused silica 
in a vein fissure, comes this again, that quartz veins fre- 
quently consist of very thin strings, of half an inch wide, or 
even less. Were it, then, still conceivable that molten 
quartz, of a foot or more in width, could rise in a fissure or 
rent, without solidifying in the course it must have travelled 
from unknown depths, yet it would be quite inconceivable 
that a mass, of scarcely half an inch in thickness, should 
flow through the cold rock without being immediately chilled. 
This were equally impossible as to attempt, by pouring 
melted iron into a channel some hundred feet long, and half 
an inch wide, to form an iron rail or plate. 
If we lay aside the notion of the production of quartz 
veins in stratified formations by the agency of a smelting 
heat, there remains no other assumption but that these veins 
have been formed by the agency of water. In fact, there is 
not one phenomenon presented by quartz veins that is incon- 
sistent with this assumption. On the contrary, every cir- 
cumstance may be explained, by its aid, in a simple and un- 
forced manner. 
There is scarcely any water, whether it’be spring or river 
water, which does not contain silica in solution, though fre- 
quently in very small quantities. Should such water pene- 
trate through the narrowest cleft, there is the possibility that 
more or less of the dissolved silica may be deposited in it. 
It is true, that such a deposition supposes that the water, 
either, being hot, cools during circulation in the cleft, or 
evaporates ; or that other substances maintaining the silica 
