227] J. T. Singewald 29 



ores crystallized out of a magma and that the forma- 

 tion of the titanif erous magnetites " depends on a pure mag- 

 matic separation, not accompanied by special pneumatolytic 

 processes," and that the process differs from ordinary rock 

 differentiation only in that it has proceeded much further. 

 The characteristic association of more or less titanomagnetite 

 with the sulphides is taken to indicate a genesis for the latter 

 ores analogous to that of the titaniferous magnetites. In 

 further substantiation of the magmatic origin of the sul- 

 phides is the statement that secondary alterations such as 

 uralitization before ore deposition or contemporaneous with 

 it has not in general occurred. They emphasize the fluidity 

 of the molten sulphides and the consequent power of pene- 

 tration into minute crevices and cracks and have proposed a 

 subdivision of injected sulphide deposits, which represents 

 intrusions of molten sulphides into the country rock. In 

 such an interpretation of a number of the most important 

 examples included under this subdivision, however, they stand 

 almost alone.' 



The deposits under discussion are classed by Lindgren as 

 " Mineral deposits^Jefmed by concentration in molten mag- 

 mas," concerning which he says : " Certain kinds of mineral 

 deposits form integral parts of igneous rock masses and per- 

 mit the inference that they have originated, in their present 

 form, by processes of differentiation and cooling in molten 

 magmas/' Of the oxidic ores he says chromite appears in all 

 cases to be the earliest consolidated constituent, but that the 

 titaniferous iron ores have as a rule crystallized after the 

 silicates ; but he says further about the latter : " Petrographic 

 research has long ago shown that ilmenite with magnetite is 

 one of the earlier products of consolidation in magmas and 

 is contained in almost all diabases, basalts, and gabbros. . . . 

 The larger masses of ilmenite are simply facies of the rock 

 itself produced by concentration from the same magma." 

 Lindgren's position concerning the sulphides is almost identi- 

 cal with that of Beyschlag, Krusch and Vogt, as is evidenced 

 by such statements as, " Some of the magmatic sulphide 



