THE BA SIC MA SSI VE RO CKS, ETC. 825 



has been described a number of times. Matthew 1 has noted it 

 in a gabbro area near St. Johns, New Brunswick, while Vogt 2 

 has described it at a large number of places in Norway, Sweden, 

 and other European countries. A notable feature in connection 

 with the phenomena described by Vogt is the association of 

 oxide and sulphide ores with the basic portions of the differen- 

 tiated rocks. Many of the magnetite deposits of Norway are 

 shown by this author to be peripheral phases of gabbro. The 

 occurrence in Minnesota is similar to the Norwegian occurrences, 

 and hence the author concludes that the ores of Winchell's 

 "gabbro-titanic-iron group" have a similar origin. It has been 

 shown by the descriptions that this is the case ; the basic aggre- 

 gates on the northern border of the gabbro area are peripheral 

 phases of the coarse-grained olivine gabbro, whose composition 

 and structure are so uniform throughout most of its extent, and 

 the ores associated with these aggregates are only more basic 

 phases of the same magma, by whose differentiation, after its 

 intrusion into its present position, olivine gabbro, pyroxene- 

 olivine aggregates, and almost pure titaniferous magnetite beds 

 were formed. 



W. S. Bayley. 



*W. D. Matthew : Trans. N. Y. Acad. Sci. 



2 J. H. L. Vogt: Bildung von Erzlagerstatten durch Differentiationsprocesse in 

 basischen Eruptivmagmata. Zeits. f. prakt. Geologie, Januar, 1893. 



(To be concluded.) 



