60 J. C. BRANNEK GEOLOGY OF NORTHEAST COAST OF BRAZIL 



tidelevel that they can not be occupied by sea-urchins. It is evident 

 that there has been a recent elevation of this part of the coast, amount- 

 ing to about 2 meters. There are many other large masses in place 

 similarly pitted. 



I recall no other occurrence of trachyte in Brazil. D'Orbigny says 

 that trachytes accompany the porphyries of the western side of the Cor- 

 dilheiras, but he adds : " No one has noted them in Brazil or in the 

 Guyanas, and I have only seen them in the Cordilheiras or on their 

 western slopes." * 



GRA NITE AT GA IB U 



South of Pedras Pretas the next rocks of interest in this connection 

 are exposed at the village of Gaibu, just north of Cabo Santo Agostinho. 

 The rocks at this place are coarse grained gray granites. They are ex- 

 posed at the foot of the hill, southwest of the village, where an old fort 

 stands on them. 



Southwest of the village of Gaibu is a high hill of Tertiary sedimentary 

 beds overlying the granite. Following the foot path across Cabo Santo 

 Agostinho, from Gaibu to the village of Suape, the granite continues 

 halfway up the hill, but the top of the ridge is of Tertiary sediments. 

 About the light-house on the cape, and especially on the north side of 

 it, are many enormous exfoliated boulders of granite. 



GRANITES AND DIORITE OF CABO SANTO AGOSTINHO 



The granite runs all the way round Cabo Santo Agostinho from Gaibu 

 to Suape in one form or another, and only on the top of the ridge are 



r 



£«A, e , '<\) 





^D/orc 



m. 



Figure 8. — Geology on South Side of Cabo Santo Agostinho. 



there patches of Tertiary sediments. f On the south side of the cape 

 are several quarries in the granite-porphyries, all of them now idle. 



* Voyage dans l'Amerique Meridionale, t. III. 3e Partie, Geologic, pp. 215-216. Paris, 1842. 



fThe rocks here spoken of as Tertiary have thus far afforded no evidence whatever of their 

 age. Their stratigraphic position and their lithologic characters would both admit of their being 

 Cretaceous quite as readily. 



