136 
AMERICAN GEOLOGY. 
INDICATIONS OF A GOOD OR BAD VEIN, JUDGED OF BY THE 
CHARACTER OF ITS WALLS. 
§ 89. The structure of a vein furnishes important information 
respecting its value, as I have already intimated. The walls, 
however, are not to be passed by unheeded. In the first place, 
we look for clear and well defined boundaries between the vein 
and wall; and if the walls are marked with what the miners 
term slickensides, which are polished striations more or less 
vertical in direction, the indications of a well-formed vein are 
sufficiently satisfactory. Sometimes, however, the walls are 
not equally well defined. We look in this case to the foot 
wall, and miners are generally satisfied if they find this hard or 
firm, and distinct from the veinstone, even if it is not marked 
with slickensides. 
As regards the indications of a well-formed vein in its struc¬ 
ture and character of its walls, we find that a porous veinstone 
furnishes the best indications, especially if the gangue, with the 
metal, is arranged in parallel stripes, the bunches elongated and 
confluent, or become more so as the shaft increases in depth. 
On the contrary, where the ore or metal is sparsely disseminated 
in a hard, compact, tough gangue, with scarcely any tendency 
to become confluent, in a veinstone of this description, the 
indications of a well-formed and productive vein are unfavor¬ 
able. So also where the vein, though tolerably distinct in parts, 
is mostly incorporated with the walls, or what are taken for 
walls, the indications are unfavorable. I have said nothing of 
the judgment we should form of the increase of metal as the 
shaft increases in depth, for it is sufficiently plain, that in this 
country, there should be an increase of metal within forty feet 
of the surface. The kinds of veinstone are numerous; and 
how much the value of a mine is dependent upon them, is not 
well determined, excepting the general fact that some are much 
softer and more workable than others, and require less expense 
in working them. 
