332 THEORIES OF ORE DISPOSITION HISTORICALLY OONSIDERED. 



Fresh as he was from his controversy with Sandberger over the 

 lateral-secretion theory, which he had disproved, at least in its appli- 

 cation to the Pribram deposits, he was inclined to view with disfavor 

 anything that flavored of lateral secretion; hence, while admitting 

 that the presence of minute quantities of the metals in eruptive rocks 

 leads to the surmise that they had brought the whole series of heavy 

 metals up from the barysphere into the lithosphere or upper crust, 

 he preferred to assume, in the cases which the American geologists 

 had explained as derivation from eruptive rocks in the vicinity of the 

 deposits, that the mineral contents had been brought up by thermal 

 waters directly from the barysphere. Likewise, in the limestone 

 deposits, which their studies show to have been formed by metaso- 

 matic replacement, he thought that they must have overlooked some 

 evidence of crustification, and still held to the opinion that such 

 extensive deposits must be mainly the filling of open spaces. Al- 

 though not explicitly stated, it is evident that he regarded the water 

 of his deep circulation as mainly of meteoric origin. 



Of great i^ractical value was the clear idea conveyed to the mind 

 of his readers of the distinction between the oxidized or altered min- 

 erals and the original or sulphide minerals of an ore deposit, a dis- 

 tinction ])reviously pointed out, though less emphatically, by Em- 

 mons " and others. 



In the same year appeared the first of a series of important articles 

 on the formation of ore deposits by the Norwegian geologist, J. H. L. 

 Vogt, in which, as opposed to Posepny's views, so much more impor- 

 tance is given to igneous agencies that their ditferent standpoints 

 recall the antagonisms of the old Neptunist and Plutonic scliools. 

 The petrographic studies of Vogt and Brogger had disclosed in basic 

 dikes a tendency of the heavier minerals to concentrate near the 

 borders. Following out the suggestion ofl'ered by this ol)servation, 

 Vogt had ])roved by field study that certain titaniferous iron ores 

 were actual segi-egations in the eruptive magma previous to its final 

 consolidation. liased on jjetrographic studies made by Brogger and 

 liimself. and personal observations on ore deposits, principally in 

 Norway, Vogt defined two methods of formation of ore deposits as 

 the direct result of igneous action : 



1. By magmatic segregation. 



2. By eruptive after-at-tion of pneumatolysis (a term first used by 

 Bunsen to describe the couibined action of gases and water). 



Tn the first class (of admittedly infrexiuent occurrence) are titanif- 

 erons iron ores, chromite, and other metallic segregations in basic 

 eruptive rocks. In the second class, commencing with tin and apatite 

 veins, he included, as time Avent on, increasingly numerous types of 



a Colorado Scientific Society, vol. ii, pt. ii, 1886, p. 99. 



