J. C. Branner — Geology of Fernando de Noronha. 145 



Art. XVII. — The Geology of Fernando de Nor on ha. Part I ; 

 by John C. Branner. With a map, Plate Y. 



The island of Fernando de Noronha has never attracted 

 much attention, owing to its small area, its want of commercial 

 importance, and its somewhat forbidding character as a land- 

 ing place, and partly also to its having long been used as a 

 place of exile and punishment for criminals. Prior to the 

 visit of the writer the geologic observations made upon the 

 island of Fernando were very few ; the only ones worthy of 

 especial notice being those of Charles Darwin in 1832, made 

 while on the voyage of the Beagle and published in his Geo- 

 logical Observations in 1844, and a few observations made, 

 along with the collection of specimens, when the Challenger 

 touched here in 1873. A careful survey would have been 

 made by the Challenger party had permission been given by 

 the Brazilian officers in charge ; but owing to the care exer- 

 cised in the supervision of the convicts and to a misapprehen- 

 sion of the objects of the survey, this permission was unfortu- 

 nately withheld. 



In 1876 I visited Fernando as a member of the Imperial 

 Geological Survey of Brazil, and the following brief notes are 

 the first to be published giving any of the results of my obser- 

 vations upon its geology. 



"With the accompanying map the reader will scarcely need 

 any observations upon the geography of this group of islands, 

 while the illustrations will convey a sufficiently clear idea of 

 the surface features of the place to dispense with detailed de- 

 scriptions of topography. 



The form of the ocean's bottom around this island, however, 

 is worthy of note as indicating the relations of the group to 

 other islands and to the Brazilian mainland. For the facts 

 bearing upon this subject we are indebted to the deep-sea 

 soundings of the Challenger expedition. It was formerly sup- 

 posed that Fernando was simply the original northeastern 

 extremity of the South American continent, now separated 

 from Cape St. Roque by a shallow channel. The deep sea 

 soundings have shown, however, that the Fernando group is an 

 isolated one, and that the channels separating it from the 

 Rocas, from St. Paul's Rock and from the Brazilian mainland, 

 are profound ones. The channel between Fernando and St. 

 Paul's Rock is more than 14,000 feet deep, while between Fer- 

 nando and the Brazilian mainland the depth is over 13,000 

 feet. To the northeast, six miles from the island, the sound 



Am. Jour. Sci.— Third Series, Vol. XXXVII, No. 218.— Feb., 1889. 

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