Making Potosi the centre of his survey and
the deposit of his collections, he executed a thorough examination of
that district, where he found some seventy mines scattered over a large
surface of the public domain, which yielded, at the utmost, by a very
desultory process, about three millions of pounds of lead annually.
Having explored this region very minutely, he wished to ascertain its
geological connection with the Ozark and other highland ranges, which
spread at the foot of the Rocky Mountains, and he planned an exploratory
expedition into that region. This bold and hazardous journey he
organized and commenced at Potosi early in the month of November, 1818,
and prosecuted it under many disadvantages during that fall and the
succeeding winter. Several expert and practiced woodsmen were to have
been of this party, but when the time for setting out came all but two
failed, under various excuses. One of these was finally obliged to turn
back from _Mine au Breton_ with a continued attack of fever and ague.
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