272 J. C. BRANNER — DECOMPOSITION OF ROCKS IN BRAZIL. 



The Pao d'Assucar or Sugar Loaf is so steep that it is barely possible 

 to ascend it only on one side — the slope on the right shown in the illus- 

 tration ; on all the other sides it is perpendicular or overhanging (see 

 also plate 10). Its steep sides are covered with little air plants, and the 

 least steep one supports patches of sticky grass (capini gordwrd), and on 

 the summit is a cluster of small trees and ferns. 



From the top of the Sugar Loaf the view of the hills and peaks to the 

 west includes almost every variet,y of topographic form to be found in. 

 the gneiss and granite regions of the Serra do Mar of Brazil. 



The Gavea (plate 12) is a flat-topped mountain 2,432 feet high (Homem 

 de Mello), about four miles west of the city of Rio, and might appear to 

 be an exception to the rule that granites and gneisses produce rounded 

 forms ; but this is more apparent than real. In general outline the mass 

 of the Gavea is as much like the other mountains around it as any other 

 peak. It is a mass of gneiss, and the banding is approximately hori- 

 zontal. The flat tojD is made In^ one great bed several hundred feet thick, 

 being a little more resisting than tlie rest of the mass. This laj^er has 

 allowed the original top to be entirely removed, but it has protected the 

 lower part of the mountain somewhat."^ 



The Corcovado is 2,329 feet high, of coarse porphyritic granite at the 

 top. On the south side it falls away almost perpendicularly a clean face 

 of over a thousand feet, while to the northwest its slope is sufficiently 

 gentle to admit of easy climbing. Exfoliation goes on now only on the 

 precipitous face, the other sides being covered with vegetation. 



Just east of the Corcovado is a rounded peak which ma}^ be taken as a 

 representative of a large number of the exfoliated gneiss hills of the re- 

 gion. It is shown in the middle in figure 3. Here the surface has flaked 

 off in great sheets that have slid down tlie mountain slopes. The angle 

 has now become so low that vegetation is rapidly encroaching ujDon the 

 mountain mass from the lower slopes and also from the cluster of trees, 

 bushes and undergrowth that crowno the summit. 



It seems invidious to mention any of the less prominent exfoliated 

 peaks about Rio. The Dois Irmaos between the Jardim Botanico and 

 the Gavea and the one on which the church of Nossa Senhora da Penha 

 stands, however, come to mind as examples worthy of special mention ; 

 the latter is near the bay, northwest of the city of Rio. No less interest- 

 ing and striking are the sharp and lofty but always rounded peaks of 

 the Organ mountains — peaks so slender that the}^ have given name to the 

 mountains in which they occur. The accompanying figure, 4, will tell 

 more of the appearance of one of these peaks than any verbal description. 



* Tlie top of the Gavea is accessible with difficulty at one point only. The summit is covered by 

 exfoliated boulders. Near at hand it is the most impressive of the rocks about Rio de Janeiro. 



