270 J. C. BRANXER — DECOMPOSITION OF ROCKS IN BRAZIL. 



Such hills often have a striking resemblance to some of the great glaciated 

 rock surfaces of the north, so round and smooth are they. Indeed, 

 Agassiz was at one time of the o^Dinion that many of those above Rio de 

 Janeiro were roches moiUonnees.'^ In other cases they resemble in outline 

 volcanic cones, f Sometimes there is one abrupt, perpendicular, or even 

 overhanging face, while the other sides slope away at a low angle. 



The faces of these bare rocks are usually so steep that ordinar}^ vegeta- 

 tion can find no foothold on them, although they are usually beautifully 

 adorned with epiphytes, and especially with little gray bromelias, bearing 

 white and pink flowers. Toward the summits on these rocks the lower 

 angles of the faces allow a little soil to accumulate, and here hardy ferns- 

 and such plants as readily withstand drv weather J quickly gain foot- 

 hold, while the summits are often crowned with bushes and even with, 

 large trees. The distribution of these topographic forms corresponds in^ 



the main with the distribution of 

 the granites and gneisses, and I 

 have never seen them in rocks of 

 an}^ other kinds. 



It is a noteworthy feature of 

 this exfoliation of peaks that the 

 flakes come to a feather edge on 

 the downhill side, so that they 

 FiGVRv. i.-n^agram iiiusiraiing i/,e E^/oUaiion overlap cach othcr Hkc gigautic- 



of Cones. ^ . . . 



scales. This is shown in almost 

 every view of these exfoliated mountains. The accompanying diagram 

 exhibits the theoretic arrangement of these crevices on difl'erent slopes. 

 These scales also wrap around the peak, as may be seen in the case of 

 the Gavca (see plate 12). On the shore at Copocabana, on the other hand, 

 these scales seem to be inverted (see plate 11). This, however, may be 

 a local accident. § 



The most striking illustrations of these forms occur in the Serra do- 

 Mar. They abound in and about Rio de Janeiro, where they give char- 

 acter to the scenery and make the bay of Rio the most beautiful and im- 

 pressive harbor in the world. At the ver}^ entrance to the bay stands 

 the Pao d'Assucar, a solid mass of gneiss more than 1,200 feet high, and 

 rising on one side straight from the water's edge. 



* Joar. Geol , Nov.-Dec, 1893, p. 768. 



t Agassiz : Journej' in Brazil, p. 69. 



X Among tiie plants quite chai-acteristic of such places are certain large species of Bromelia 

 whose equitant leaves serve as receptacles and reservoirs for the rain and dew and thus supply 

 them with abundant moisture even when the soil is almost entirely wanting. 



§ I am indebted to Mr Edward S. Benest, of Rio de Janeiro, for the photograph of the Copocabana. 

 rock, and for several others illustrating this paper. 



