Joseph LeConte—Genesis of Metalliferous Veins. 7 
theory which connects vein-formation with solfataric action is 
wholly a levigation theory. According to this theory as I un- - 
derstand it, the vein matters including the metallic ores are not 
derived from an unknown mysterious region of volcanic fires, 
but are gathered by leaching from the whole wall rock from top 
to bottom of the fissure; but mainly from the deeper parts, be- 
cause these are under heavy pressure and superheat. Subterrane- 
an waters gathering soluble matters from wide areas and great 
thicknesses of rock find their way into fissures, and these then 
become their natural channels back to the surface from which 
they come. The theory may be formulated as a depositing of 
materials, mainly in the return course of circulating meteoric 
waters. The 
veins and amygdules. The reason is obvious. In true metal- 
liferous veins the surface country rock is a factor, true: but 
escence inconsistent with the idea of water issuing in springs. 
But evidently the quiescence can be only relative. Some move- 
