ON NEPHELISTE-ROCKS IN "BRAZIL. 



457 



33. On Nepheline-Rocks in Brazil, iviih Special Reference to the 

 Association of Phonolite and Foyaite. By Orville A. 

 Derby, Esq., F.G.S. (Read June 22, 1887.) 



The nepheline -rocks heretofore recognized in Brazilian territory 

 are the phonolites and associated basalts of Fernando Noronha, a 

 deep-sea island off the north-eastern shoulder of the continent, in 

 lat. 3° 5' S„ long. 32° 24' 19" W., the volcanic nature of which 

 appears to have been first recognized by Darwin in the ' Voyage of 

 the Beagle'*. Recently a single small pebble from the little- 

 known island of Trinidade, in lat. 20° 31' S., long. 29° 19' W., has 

 come into my hands, showing that phonolite of somewhat different 

 character from that of Fernando Noronha occurs at that place 

 also. 



Recent investigations have shown that nepheline-rocks of a 

 somewhat different character are also abundantly developed on the 

 mainland, and in such favourable conditions as to throw light on 

 the relations of the granitic type of foyaite or eheolite-syenite to 

 the other members of the group. The localities in which they have 

 thus far been recognized are situated in the Provinces of Rio de 

 Janeiro, Sao Paulo, and Minas Geraes, and their relative position 

 and relation to the main orographic lines of the region in which 

 they occur are shown in the accompanying sketch map (fig. 1). Three 

 of these localities, Carnpo Grande, Cabo Frio, and the peak of Tingua, 

 are in the immediate vicinity of Rio de Janeiro, the latter being in 

 the Serra do Mar range, the two former among its foot-hills. 

 Further south another set of localities occurs in the same range 

 in the valley of the river Iguape. In the Mantiqueira range the 

 peak of Itatiaia (3000 metres high, and the highest mountain of 

 eastern South America) and one or more other high peaks in the 

 neighbourhood are composed of these rocks, which occur also in the 

 Serra do Bocaina, a spur of the Serra do Mar range on the opposite 

 side of the Parahiba valley. The other two localities are the Pocos 

 de Caldas (hot springs), on the southern margin of the great 

 westward expansion of the mountainous area which connects the 

 coast range through the Serra do Canastra with the central range 

 of Goyag, and Itambe in the Serra do Espinhaco range, a northward 

 extending branch of the Mantiqueira. As little more than a year 

 has elapsed since attention was first directed to these rocks, and as 

 the first knowledge of their existence in these different localities 

 was obtained almost casually, it may reasonably be supposed that 



* A few of the Fernando-Noronha rocks are described by Eenard (Bull, de 

 l'Acad. de Belgique, iii. 1882). A very complete collection made by Mr. J. C. 

 Brainier for the Geological Commission of Brazil has been placed in the hands 

 of Prof. Gr. H. Williams for study. 



