of its two g-eologists, Mr. Orestes H. St. John being the 

 other. This expedition left New York in April, 1865, 

 and returned in July, 1866, having been absent a little 

 more than a year. This was the strong and final induce- 

 ment that called Hartt away from the geology of his own 

 country. Although he was not fortunate in finding a very 

 rich geological territory during his wanderings, while 

 connected with the Thayer Expedition, he saw enough 

 to thoroughly interest him in returning again to Brazil, 

 and in finally giving his whole attention to Brazilian 

 studies. There is little necessity for going minutely 

 over the details of his first few trips to that country. 

 Accounts of them have been published, and are easily 

 accessible. 



The primary object of the Thayer Expedition was the 

 investigation of the distribution of the fresh-water fishes 

 of Brazil, but much time was also devoted to the study 

 of its geology. No new fossiliferous deposits or localities 

 were discovered, and of those already known, only the 

 Cretaceous at Bahia, and the Post-Pliocene of Lagoa 

 Santa, were visited. Professor Agassiz limited himself 

 mostly, in his geological work, to the examination of the 

 superficial deposits at Rio de Janeiro and on the Ama- 

 zonas, which were studied in connection with the ques- 

 tion of glaciers. Hartt was retained near Rio for some 

 time, in making examinations of the many cuttings 

 ai'ound that city. After this work was completed, his 

 field of exploration lay mostly between Rio and Bahia, 

 where, with Mr. E. Copeland, of Boston, as a companion, 

 he carefully studied the geological and other features of 

 the coast, and of the principal river basins leading to it. 

 Large collections of the fresh water fishes of the rivers, 

 and of the marine animals of the coast and reefs, were 

 made. The region from Rio to Bahia is entirely meta- 

 morphic, consisting mostly of gneisses, covered in large 

 part with loose or only partially consolidated materials, 

 without fossils. In consequence of this absence of 

 fossils, no results in systematic geology were obtained, 

 but, nevertheless, Hartt's studies of the geology of this 

 2 



