Charles Frederick Hartt. 119 



two geologists, 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 inducement 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. 



The primary object of the Thayer Expedition was to in- 

 vestigate the distribution of the fresh water fishes of Brazil, 

 but much time was also devoted to its geology. Prof. Agassiz 

 limited himself mostly, in his geological work, to the 

 examination of the superficial deposits at Eio de Janeiro 

 and on the river Amazon, which were studied in connection 

 with the question of glaciers. Hartt was retained near Bio 

 for some time, in making examinations of the many Bail- 

 road cuttings around that city. After this work was com- 

 pleted, his field of exploration lay mostly between Bio and 

 Bahia, where he carefully studied the geological and other 

 features of the coast, and of the principal river basins lead- 

 ing to it. Large collections of the fresh water fishes of the 

 rivers, and of the marine animals of the coasts and reefs 

 were made. In consequence of the absence of fossils, no 

 results in systematic geology were obtained, but, neverthe- 

 less, Hartt's studies of the geology of this monotonous tract 

 were of areat interest. 



In the neighborhood of Porto Seguro he explored the 

 coral and sandstone reefs, the latter of which is a promi- 

 nent feature of the Brazilian coast. He was the first to 

 carefully work out the structure and mode of formation of 

 these sandstone reefs. 



After Hartt had returned to the United States from the 

 Thayer Expedition, he felt that he had left unfinished some 

 of the more important investigations he had made in Brazil. 

 He was unable to report as fully as he wished, on many 

 subjects of interest which he had partly studied. So in 1867 



