470 (7. K Hartt— Geological Survey of Brazil 



Sao Francisco. This river once ran over these beds at a height 

 of one thousand feet, more or less, above its present level, exca- 

 vating its channel in the sandstone until it had cut through to 

 the gneiss. Above the rapids the river now courses almost over 

 the surface of the plain, its channel being but slightly indented ; 

 but upon arriving at the rapids it is suddenly precipitated by a 

 series of magnificent waterfalls through an exceedingly narrow 

 gorge, the depth of which immediately below the rapids is from 

 80 to 90 meters. This gorge, or canon, with its walls nearly or 

 quite vertical, extends as far as Piranhas, the river in this por- 

 tion being much broken by rapids. Below Piranhas the river 

 valley still maintains its canon-like character, although its width 

 is increased. 



Like Niagara, these falls are slowly retroceding, but in a dif- 

 ferent manner. ***** 



At the Cachoeira de Paulo Alfonso the water passes over 

 gneissic rocks. These do not here suffer decomposition or disin- 

 tegration by frost, but they are much eroded by transported sand 

 and stones, which produce extraordinary effects, by excavating 

 innumerable pot-holes that soon communicate and allow masses 

 of the rock to fall away. In my final report, the region of the 

 cachoeira will be very carefully described, as well as the geology 

 and physical geography of the lower Sao Francisco. 



We returned to Pernambuco at the end of six weeks, and a 

 few days later the bulk of the collections, filling sixty large boxes, 

 were sent to Rio de Janeiro. 



Dr. Jordao becoming ill at this juncture, I permitted him to 

 return to the capital [Rio.] As my two assistants, Messrs. Derby 

 and Rathbun, had not yet arrived, and beginning to feel the need 

 of help, I called upon my former assistant, Mr. John Caspar 

 Branner, who, being then in Rio, came at once to my aid, per- 

 forming very valuable services. He is still employed by the 



After shipping the collections, I returned to Maria Farinha, 

 with Dr. Freitas and Mr. Branner, in order to finish the study of 

 the Cretaceous beds and to examine the coral reefs. In ten days 

 we returned again to Recife [another name for the city of Pernam- 

 buco] with a large vessel loaded with fossils, etc. Having been in- 

 formed that your Excellency desired to exhibit some of the re- 

 sults of the Commission at the National Exposition [held at 

 Rio Janeiro, January, 1876] the new collections were packed m 

 seventy more cases, and I returned with them to the capital in 

 December, accompanied by Senhor Ferrez. * 



While at Pernambuco, I procured a large barque from Mr. 

 Frederico Soares, of Maria Farinha, and sent Dr. Freitas and Mr. 

 Branner to explore the geology of the coast and its reefs as tar as 

 Parahyba do Norte,— a trip which was made with good results. 



