Origin of Mineral Veins 79 
ment of the minerals is very different. The deposition of 
various spars one on the other in cavities is a secondary 
operation even now going on, and has nothing necessarily 
to do with the original filling of the lodes; indeed, their 
arrangement is so different that it helps to prove they have 
been differently formed. 
It would take a volume to discuss this question in all its 
bearings, and as I have already entered more fully into it in 
another place,! I shall only now give a brief résumé of the 
conclusions I have arrived at respecting the origin of mineral 
veins. 
1. Sedimentary strata have been carried down, by move- 
ments of the earth’s crust, far below the surface, covered by 
other deposits, and subjected to great heat, which, aided by 
the water contained in the rocks and various chemical re- 
actions, has effected a re-arrangement of the mineral contents 
of the strata, so that by molecular movements, the meta- 
morphic crystalline rocks, including interstratified granites 
and greenstones, have been formed. 
2. Carried to greater depths and subjected to more intense 
heat, the strata have been completely fused, and the liquid 
or pasty mass, invading the contorted strata above it, has 
formed perfectly crystalline intrusive granites and green- 
stones. 
3. As the heated rocks cooled from their highest parts 
downwards, cracks or fissures have been formed in them by 
contraction, and these have been filled from the still-fluid 
mass below. At the beginning these injections have been 
the same as the first massive intrusive rocks, either granite 
or greenstone; but as the rocks gradually cooled, the fissures 
reached greater and greater depths; and the lighter con- 
stituents having been drawn off and exhausted, only the 
heavier molten silica, mingled with metallic and aqueous 
vapours, has been left, and with these the last-formed and 
deepest fissures have been filled. These injections never 
reached to the surface—probably never beyond the area of 
heated rocks; so that there have been no overflows from 
them, and they have only been exposed by subsequent great 
upheaval and denudation. 
4. Probably the molten matter was injected into the 
1 Mineral Veins, by Thomas Belt. John Weale, 1861. 
