274 J. C. BRENNER — DECOMPOSITION OF ROCKS IN BRAZIL. 



The Serra de Macahe east of Nova Fribiirgo is characterized by the- 

 peaks and cones resembling those about Rio de Janeiro, '^Myhile from 





mm 







Petropolis along the Uniao e Industria road toward Juiz; 

 de Fora and be\'ond almost to Sitio (north of the crest 

 of the Serra da Manticpieira) the domed peaks and ex- 

 foliating cliffs give character to the landscape, f The 

 Pedra de Parahybuna, near Juiz de Fora in Minas Ge- 

 raes, is a fine example of the exfoliation of a massive 

 rock. Dome-like summits are also character- 

 ^ istic of the gneiss and granite areas in the dia- 

 mond district of Minas. X 



Itatiaia, the noted high mountain 

 in the west end of the state of Rio de 

 Janeiro, has the rounded outHnes 

 and exfoliate boulders produced by 

 concentric weathering of massive- 





Figure ^.—Dedo de Dens. 



Gneiss peak near Theresopolis, Organ 

 mountains, Brazil. 



rock. § 



Along the coast east and northeast 

 of the bay the topography is in the main 

 a repetition on a small scale of that 

 about Rio de Janeiro. 



Cape Frio is of crystalline rock (foy- 

 ite), and though the upper portions are- 



* Reise nach Brasilien. H. Burmeister. Berlin, 1853, pp. 139, 177, 178. 



t Notes of a Naturalist in South America. John Ball, 1887, p. 314. Bermeister : Reise nach- 

 Brasilien, p. 520. 



X Ueber das Geognostische Vorkommen der Diamanten. Virgil v. Helmreichen. Wien 184G, p. 7. 



§ Descrip95o do Itatiaia. Por Jos6 Franklin da Silva. Revista do Inst. Hist, do Brazil, xxix, pt. 

 i, pp. 413-418. ExcursOes Geographicas. Pelo Barilo Homem de Mello. Revist Inst. Hist., li, pt. 2» 

 pp. 167-178. Derby says Itatiaia is nephelene syenite instead of granite, as others have stated^ 

 Quar. Jour. Geo!. Soc, 1887, xliii, p. 457. 



