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ME. 0. A. DERBY OK 



future investigation will give them a very considerable extension 

 beyond the limits above indicated *. 



At the Cabo-Frio locality, a rocky island about three miles long 

 and 400 metres high is composed almost exclusively of foyaite of 

 two distinct types, the least abundant of which is referred by Prof. 

 Sosenbusch, who has kindly undertaken a microscopic examination 

 of these rocks, to nepheline-bearing augite- syenite. A single point 



Pig. 1. — Sketch Map of parts of the Provinces of Rio de Janeiro, 

 Sao Paulo, and Minas Geraes. 



of the island is occupied by a considerable mass of felspathic tuff. 

 The adjoining mainland is composed of gneiss cut by numerous dykes 

 of phonolite, basalt, amphibolite, diabase, and other rocks. A 

 detailed description of this important locality is deferred for a 

 future paper. At the Campo-Grande locality a network of dykes of 

 diabase, phonolite, trachytes, and various kinds of basalt, one of 

 which is limburgite, occur in gneiss in the railway-cuttings. Judging 



* Since the above was written, I find the occurrence of nepheline basalt 

 reported by Pohlman from Paraguay ('Neues Jahrbuch,' 1886, vol. i. p. 244), 

 which makes it probable that the group of rocks here considered will be found 

 also in the Brazilian highlands bordering the Paraguay basin. 



