VOLUME XXIX NUMBER 6 
THE 
MOURNAL OF GEOLOGY 
_ SEPTEMBER-OCTOBER 1021 
THEORETICAL CON SIDERATIONS OF THE GENESIS 
OF ORE DEPOSITS 
R. H. RASTALL 
Cambridge University, England 
Nothing is more noticeable in the history of mining geology 
than the change which has taken place in the last half-century in 
the prevailing opinions as to the origin of ore deposits. We may 
leave out of account the absurdities of Wernerism and most of the 
earlier speculations of the Plutonist school. Scientific ideas as to 
the genesis of ores may be said to date from the publication of 
Breithaupt’s epoch-making little book in 1849. Here in the idea 
of paragenesis we have the germ of modern speculations on this 
subject. For long, however, the theory of the aqueous origin of 
all ore deposits held sway in its various forms, one of the best- 
known of which was the famous lateral-secretion theory. Even 
yet something very like this theory is held to furnish the best 
explanation of the origin of certain types, as for example the lead- 
zinc ores of the Mississippi Valley and other similar deposits. 
The brilliant writings of PoSepny also did much to perpetuate the 
reign of water. Nevertheless, at the present time no one will be 
found to deny that many and important ore deposits are of direct 
igneous origin. As a matter of fact igneous and aqueous origin 
are by no means incompatible. It may at once be admitted that 
watery solutions may be produced direct from magmas. Of this 
t Breithaupt, Die Paragenesis der Mineralien, Freiberg, 1840. 
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