172 
The American Geologist. 
September, 1902 
ness. etc., of the rocks, the fissures found in them will vary in 
character, and the physical aspect of any resultant ore-deposit 
will be governed by the nature of the rock. 
Fissure-veins, and, indeed, all forms of ore-deposits, are af- 
fected in size and shape, and probably to some extent in rich- 
ness, by the character of the fissure or fracture in which the 
vein was formed. Experience shows that a vein often varies 
greatly in structural characters, such as width, uniformity, 
presence of splits and horses, etc., in passing, whether horizon- 
tally or verticallly, from one rock into another. Thus the vein 
may pinch out in a very tough rock, expand in a more easily 
shatterefl material, become dissipated into a stockwork in 
brittle, shattered rock, or become lost entireh' in a shale. In 
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Scattering of the Gottlob Vein in Quartz-Poriihyry, in the David Shaft, 
near Freiberg, Saxony. .^^ Gray Gneiss;/, Quartz-I^orphyry; w,A'ein. 
easily soluble rocks, like limestones and dolomytes, the original 
character of the fissure may be modified by solution, and thus 
the original effects of its force may be masked. This case stands 
in such intimate connection with the mineralogical effects due 
to the nattire of the rock that it is best considered in the second 
part of this paper. The irregular deposits formed in limestones 
show the influence of the enclosing rock on the form of the 
deposit to an even more marked degree than fissure-veins. 
The fissures which, in traversing a tough rock, are clean cut, 
may, in passing into a more easily fractured rock, or one netted 
by fine jointing, produce a mass of shattered material in which 
the mineral is so disseminated in minute and numerous fissures 
that the entire mass must be extracted. Often the vein, solid 
