14. Joseph LeConte—Genesis of Metalliferous Veins. 
depositing metalliferous vein matters have been hot. Such un- 
doubtedly they were in most cases. Metalliferous veins are 
usually associated with vicinity of dykes and other evidences 
of igneous action. They are usually associated with tilting, 
folding and metamorphism of the rocks. The water cavities of 
vein stones have often a vacuous space, showing that the water 
has cooled and contracted since the veinstone was consolidated. 
We find deposits of vein matters, both matrix and metallic ore, 
now going on in hot alkaline tae and therefore presumably 
they were deposited from similar waters in previous epochs. 
But heat is evidently not siaaiaey in all cases. For example, 
(a) deposits of iron, as we know, often belong aA ne oe Be 
ferent category. This metal may indeed be n found i 
veins, and is then probably deposited like ot vein biatals: 
but it is deposited also, and more abundantly, in beds, being 
leached out of rocks and soils by solutions of organic matter at 
abundantly in undisturbed regions and in unchanged, even 
fossiliferous, strata, mostly limestones. In the lead reaies of 
Illinois, Towa and Missouri, for example, it occurs in fossilifer- 
‘ous Paleozoic limestones, in immense deposits, partially or 
wholly filling irregular cavities of great extent between the 
strata and between the joint-blocks iB ash veins). The cavities 
have been odes, like cavities in limestones everywhere, firs 
by shrinkage, and then enlarged by the solvent power of water 
containing CO, The lead sometimes wholly fills the shrinkage 
cracks, but often these have been enlarged by solvent power of 
water to veritable caves. In such cases a red clay, the residue 
of a solution of impure limestone, is found associated with the 
asda in the cave.* That lead in these cases was deposited 
rom solution is certain; that the solutions were alkaline sul- 
phides is probable; but ‘that the solutions were hot seems im- 
probable. (c) Lastly, small cracks produced by crushing of the 
rocks, and smal] vacant spaces of any kind, such as fossil-cavi- 
ties, vapor-cavities, ete., are filled ‘by reolating waters at 
ordinary temperatures. This is so well known that further 
mention of these is unnecessary. These also may be, although 
will 
Ed ee “Metallic Wealth,” p. 410 et seg. I can also confirm this from 
personal observation. : 
