CHAPTER II

THE FORMATION OF DEPOSITS OF USEFUL
MINERALS

Tue sparcity and local distribution of ores (cf. p. 4)
suggested to the earliest students of ore deposits that they
must be formed under exceptional conditions. The sea
contains in solution most of the metals that are found in
the crust; but if the ores were derived from sea-water, as
has often been suggested, they should be more widely distributed
 in marine deposits. Most ores do not occur under
conditions that indicate a marine origin. Tin is associated
with hot acids appropriate to great depths below the earth's
surface, mercury with rocks shattered and displaced by
mountain-forming movements, and primary gold with
igneous intrusions.
History oF Stupy oF Ores—The scientific study of ores
was begun in southern Germany. In the eleventh century
the chief mines in Europe were those of lead and silver in
the Harz Mountains in central Germany. The tyranny of
a local duke drove some miners to Saxony, where in 1160
they founded a free settlement—Freiberg. They there
discovered mines richer and with more varied metals than
those of the Harz; the district was called the Erzgebirge
(Ore Mountains), and the working of its complex ores laid
the foundations of modern mining and metallurgy. These
ore-veins descend steeply into the earth and as a rule become
poorer and thinner and subdivide downwards. As in the
human body many veinlets collect the blood and lead it
into the main veins, so the veins of ore were attributed to
many veinlets having collected some metal-bearing fluid
on its ascent through the earth's crust. Agricola (De Re
Metallica, 1556) established the first scientific mining school

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