156 J. C. Br miner — Geology of Fernando de Noronha. 



Ilha Rapta, the most northeastern of this group of islands, 

 appears to be made up for the most part of basalt, these rocks 

 forming its highest portion and its eastern and western 

 extremities. At its east end the basalt is rudely columnar 

 along steep shores 120 feet high ; but generally there is a 

 broken slope to the sea, covered, above the reach of the waves, 

 with talus and earth. The western point, about the Espigao, 

 is composed of nepheline-basalt (No. 72.) 



The slender neck forming the northeastern promonotory of 

 the main island, appears to be of basalt. The weathering of the 

 rocks at the exposures upon this neck, and especially upon the 

 southeast side, is characterized by extensive exfoliation and a 

 consequent disintegration of the body of the rock walls into 

 great, black, approximately round bowlders. As these masses 

 lie in place they have the appearance of a gigantic rude stone 

 wall built of black bowlders of various sizes. When they fall 

 and come within the reach of the waves, though excessively 

 hard, they are soon smoothed and rounded. The beach on the 

 north side of this neck is covered by vast numbers of these 

 black rounded stones, here facetiously known as " ooragoes de 

 negro " — negro hearts. Large blocks of nepheline-basalt (No. 

 45) cover the summit of the Morro Francez. 



It seems probable that, with a few exceptions, the basaltic 

 rocks are continuous from the extreme northeast point of the 

 main island along its eastern and southern side to the bay next 

 east of the Atalaia Grande, though but few of the specimens 

 collected upon this portion of the island seem to have been 

 preserved. It should be mentioned, however, that the great 

 deposit of tuff which forms the higher portions of the shore, 

 just east of the Morro Francez, contains loosely consolidated 

 fragments of many varieties of rocks, among which are augitite 

 (No. 115). The next extensive exposure of basalt (nepheline- 

 basalt) is in the horizontal beds which form the southwest 

 shore of the island from the cape at the Laja just west of the 

 Bahia do Sueste to the Morro Branco, a distance of more than 

 a mile. These basalts have the appearance, from a distance, of 

 being horizontally stratified sedimentary rocks. The upper- 

 most bed along this escarpment is of nepheline-basalt (No. 27), 

 while the underlying beds resemble this in gross structure. 

 (Nos. 28, 29, 30). The lower beds contain amygdaloidal cav- 

 ities, as do also some of the basalts about the eastern extremity 

 of the main island, notably at the mouth of the stream called 

 Cuyeira. 



Some of the rocks of the basaltic type occur next the base of 

 Atalaia Grande on the south side, but on account of the soil 

 which covers this part of the island it was not possible to 

 determine satisfactorily their relations to the phonolites which 



