LEAD BEARING ROCKS OF THE UNITED STATES. 
177 
of metal. This mine, which was opened in 1836, although it 
presented a fair prospect of yielding large dividends to the 
owners, yet was abandoned after three or four years’ trial. This 
arose from great extravagance and unskillfulness in mining. 
The work was prosecuted by opening the vein for a great dis¬ 
tance along its outcrop, which exposed it to inundation from 
surface water. 
To exhibit the plan pursued in opening and working this 
mine, I have copied the following diagram, Fig. 46, by which 
it will be seen by the darkly shaded parts of the figure how 
much galena has been taken out of the mine. 
Fig. 46. 
It will be observed that this shaded part extends the whole 
distance along the outcrop. Where there should have been at 
most two shafts, there is a trench extending the length of the 
vein as far as worked, some twenty or thirty feet deep, the 
effect of which is to convert what should have been closed into 
an open way for the ingress of water, which, in some cases, 
would totally ruin a mine. 
The most important lead-bearing rocks of this country be¬ 
long to the western states, Illinois, Missouri, Iowa and Wiscon¬ 
sin. The lead of these states belongs mostly to one rock, the 
Cliff limestone of the western geologists, the lower part of 
which is equivalent to the Niagara limestone of New York. 
Lead is also found in the calciferous sandstone, the lowest 
limestone of the Silurian system. In New York, this lower 
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