Charles Frederick Hartt. 
9 
two geologists, Mr. Orestes H. St. John being the other. 
This expedition left [N'ew 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 Eio 
for some time, in making examinations of the many Eail- 
road cuttings around that city. After this work was com- 
pleted, his field of exploration lay mostly between Eio 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 s^^stematic geology were obtained, but, neverthe- 
less, Hartt’s studies of the geology of this monotonous tract 
were of great 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 186^7 
