John MacCulloch

“ The shifting of veins on a small scale is much more common than the larger phenomena of this nature, which are nevertheless of frequent occurrence wherever veins exist. These larger dislocations are known to arise either from the lateral motion or subsidence of the containing parts, the sides of the line of fracture sometimes remaining in contact, and being at others separated by a vein of another description, too well known among miners to need any comment here. ”

“ Such cavities being formed the process of infiltration commences. The water existing in the rock percolates into the cavities, sometimes forming crystals, and sometimes filling the cavity with a solid mass of the matter which it held in solution. When silica exists in the rock, veins of quartz are thus formed; when lime, calcareous spar.
The solution of these earths in water is unquestionably more perfect in nature and the solutions more saturated than those which we can produce in our laboratories. ”

“ The gradual formation of quartz veins is too slow perhaps to be witnessed, but it may be conjectured from the various states in which they are seen, sometimes forming a detached and distinct crystallization, at others a solid mass, and visible more particularly in the schistose rocks. In limestone, the progress being more rapid, is more obvious. ”