230 University of California Publications in Geology [Vol. 13 



In a later paper 28 Bell states that the ores have possibly been modified 

 by aqueous solution. 



Barlow at about the same time published an almost identical theory. 

 He recognized three modes of occurrence for the sulphides. These 

 are: (1) at contacts of diabase and gabbro against other rocks; (2) 

 impregnations throughout the diabase and gabbro ; (3) in veins sub- 

 sequent to (1) and (2). The disseminated sulphides, while common 

 in the basic igneous rocks, are absent from the clastic wall rocks at 

 any great distance from the diabase and gabbro, and the sulphide- 

 bearing veins are said to be rare. 29 



Von Foullon published an account of the Sudbury deposits in 

 1892. His theory of origin 30 is in no way different from that of Bell 

 and Barlow. 



In the following year Vogt published his work on the ' ' Formation 

 of ore deposits through differentiation processes in basic irruptive 

 magmas." 31 He discusses not only the nickeliferous pyrrhotite de- 

 posits but also those of titaniferous magnetite, magnetite, ilmenite, 

 chromite, etc. Vogt concluded that the nickeliferous pyrrhotite de- 

 posits are border facies of the accompanying igneous rocks and that 

 their position at the borders of the irruptive masses is due to the fact 

 that the sulphides as a liquid differentiate have been concentrated 

 against the cooling surfaces, following Soret's principle. 32 The fol- 

 lowing is a summary of the observations which led to his conclusions : 



(1) The numerous deposits of nickeliferous pyrrhotite, in basic irruptive 

 rocks, are of world-wide distribution. They form both mineralogieally and 

 geologically a sharply bounded "world group" whose mineralogy is so simple 

 and monotonous that we may discuss in common the collected occurrences of 

 the whole world.33 



(2) From the constant relation of the nickeliferous pyrrhotite deposits to 

 basic irruptive rocks, it follows that they stand genetically in a regular rela- 

 tionship to the rock in question. s* 



(3) The nickeliferous pyrrhotite deposits are often united to the irruptive 

 rocks by gradational, petrographic transitions, to such a degree that one may 

 draw the conclusion that the sulphide masses are not later penetrations into 

 the irruptive rock, but that they were already present during the solidification 

 of the rocks. 35 



(4) The norite magmas with which the ores are associated generally show 

 a wholly extraordinary inclination to often very considerable splitting or dif- 



=s Bell, Geol. Surv. Can., Ann. Eeport, 1890-91, pt. F, p. 50. 



20 Barlow, A. E., Geol. Surv. Can., Ann. Eept., 1890-91, pt. S, p. 122. 



so Foullon, H. B. von, Jahrb. d. k. k. R. A., XLIII (1892), p. 223. 



si Vogt, J. H. L., Zeit. f. prakt, Geol., vol. 1, 1893. 



32 Ibid., p. 265, pp. 271-283. 



si Ibid., p. 126. a Ibid., p. 262. 35 Ibid., p. 262. 



