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 dis- 
tributed 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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