EARLIER EXPLORATIONS. 7 



sors the geological features of his route, and mentions the occurrence of 

 well known Cretaceous fossils from the headwaters of the Missouri to the 

 mouth of the Big Sioux; and the great geologist Von Bach, from his obser- 

 vations, was led to state, "that this great river flows uninterruptedly from 

 the foot of the Rocky Mountains, through strata of chalk, at least as far as 

 the mouth of the Sioux River. This is the result of the accounts and col- 

 lections of Prince Neuwied and of the report of the celebrated astronomer 

 Nicollet." * 



In 1839, the geographer J. N. Nicollet, under the auspices of the War 

 Department, ascended the Missouri River as far as Fort Pierre, and though 

 his travels did not extend so far as his predecessors', from his accurate 

 observation we obtained the first definite and reliable information of the 

 geology of that region. Devoting considerable time to the study of this part 

 of the Missouri Valley, he collected a large series of fossils from the Creta- 

 ceous formation, and, on his return to Philadelphia, they were described by 

 Conrad and Morton, and published in the Proceedings of the Academy of 

 Natural Sciences. The results of his explorations were published by au- 

 thority of the government. 



Mr. Audubon, in his expedition to the mouth of the Yellowstone in 1843, 

 was accompanied by Mr. Edward Harris, who had been instructed by the 

 Philadelphia Academy of Natural Sciences to make observations on the 

 geology of the region. The committee apointed by the Academy to report 

 on the notes and collections of Mr. Harris, consisting of Professors Rogers, 

 Morton, and Johnson, gave the first intimation of the proofs of the fresh- 

 water origin of certain deposits of the Upper Missouri. Previous explor- 

 ers, though recording the presence of lignites, &c. on the Missouri River 

 above Fort Clarke, never recognized the different- character of the deposits 

 above and below this point; and in the collection of Mr. Harris the first 

 proofs are presented of the great lignitic and fresh-water Tertiary beds, which 

 occupy such large areas on the Upper Missouri. Mr. Harris obtained at one 

 point " a brown, ferruginous, argillaceous rock, containing three or four 

 specimens of freshwater, univalve shells, Limnaa, Planorbis, etc. One of the 

 specimens of Planorbis, it is conjectured, may be a form extinct, but the 



* Sillhnan's Journal, September, 1850. 



