12 S. F. EMMONS — THEORIES OF ORE DEPOSITION 



fessor Oken, of Jena, who, in his text-book of Natural Philosophy (1809), 

 assumed that the earth was a polyeder formed according to the laws of 

 crystallography, and that veins or fissures resulted from the loss of the 

 water of crystallization. For the genesis of ores, darkness, earthy water, 

 and air are necessary ; hence there can be no ore in the interior of the 

 earth, since no air reaches it, etcetera. Or, again, that of Breislach, the 

 Italian geologist (1811), who put forth a Plutonic earth- theory which 

 supposed that, while the rocks were still in a molten condition the metals 

 had a tendency to separate under the influence of specific gravity and 

 of certain chemical and physical affinities, and localized themselves in 

 veins without entirely separating from their country rock. This is ap- 

 parently the first enunciation of the modern theory of magmatic segrega- 

 tion. The metallic grains in placers he supposed to have been granu- 

 lated like slag on coming in contact with water. 



The peculiar views of Werner naturally held sway longer in Germany 

 than elsewhere, yet it was his favorite pupils that were first led, in their 

 widening fields of observation, to abandon his theory that basalt is of 

 aqueous origin, though altered by the heat produced through the com- 

 bustion of neighboring beds of coal. 



Von Buch, for a long time the leading geologist of Germany, was per- 

 haps the first to whom doubts came as to the correctness of his master's 

 teachings, while studying an eruption of Vesuvius in 1799, though he 

 refrained from immediate publication of these doubts. 



D'Aubuisson, the French geologist, after visiting, in 1804, the volcanic 

 regions of Auvergne, also became convinced of its igneous origin and 

 published a recantation of the views maintained in his essay of the previ- 

 ous year on the aqueous origin of the basalts of Saxony. Finally, von 

 Humboldt (1810), perhaps the greatest of his pupils, in his extended 

 observations in the Cordilleran system of the American continents, traced 

 a direct connection between metallic deposits and the eruptive rocks. 



Observation must have convinced many of Werner's pupils of the 

 untenability of his peculiar views on the formation and filling of veins 

 long before their final refutation was published by his successor, von 

 Beust, in 1840, but reverence for his memory doubtless prevented a 

 definite expression of their opinion in print. 



Von Herder, in his work on the Meissner adit, published in 1838, 

 classified the various theories on the origin of veins that had been held 

 up to that time, as follows : 



1. Theory of contemporaneous formation (with the enclosing rock). 



2. Theory of (filling by) lateral secretion, or by material derived from 

 the enclosing rocks. 



3. Theory of (filling by) descension, or filling from above. 



