THE AGE OF THE LIGNITIC FORMATION BY ITS FAUNA. 21 



^ 3. — Tlie age of the Lignitic as indicated by its geological distribution and 



its fauna. 



The first explorers of the Great Lignitic seem to have recognized it as 

 Tertiary; for in their narration, Lewis and CUirkc mention that it overlies the 

 Cretaceous series. The definition of the age is, however, not positively ascer- 

 tained by the fossils which they collected from the upper part of the Creta- 

 ceous clay bed, where the coal scams commence, nor by those procured 

 later by Nicolet from the same locality, for they were determined by Dr. S. 

 G. Morton as Cretaceous.* Taylor asserts, however, that from specimens of 

 plants and animals from the vicinity of Fort Union, near the confluence of the 

 Yellowstone and Missouri Rivers, they derive incojitestable proofs of a fresh- 

 water formation. Taylor adds that the Upper Missouri Valley has yet to 

 receive examination from scientific geologists, and that there can be no 

 doubt but highly interesting results would follow from investigation in a field 

 so rich and extensive. On the report of Mr. Harris, the associate of Audu- 

 bon.t who ascended the Missouri to the mouth of the Yellowstone River, the 

 committee to whom this paper was referred close their reports with the re- 

 mark that the proofs thus afforded of a probably widely diffused fresh-water 

 formation in the region of the Upper Missouri, reposing upon the Cretaceous 

 strata, and imbedding remains of a manifestly Tertiary age, are just at this 

 time invested with considerable interest, from their according with the discov- 

 eries, recently made by Captain Fremont, of the presence of other and probably 

 extensive fresh-water Tertiary strata in the Oregon Territory.^ Taylor him- 

 self, considering the brown-coal formations of the Northwestern Territories, 

 calls them Tertiary. 



Dr. Hayden rightly remarks, in the beginning of his report of 1874, that 

 prior to the time when he began his explorations in 1854, the observations 

 that had been made by various travelers in regard to the existence of coal 

 beds in different jiarts of the West were of so indefinite a character that they 

 cannot be used as evidence, though they may form a part of the early history 

 of discovery. That the conclusions to which he arrived from the first on the 

 Tertiary age of the Lignitic are not based upon superficial examination is 

 sufficiently known by the numerous memoirs published by him from 1857 to 



* Proceedings of Academy of Natural Sciences of Philadelphia, October, 1841. 

 t Proceediiit;8 of tlio Academy of Natural Scieuces of Pbiladclplua, May, 184r). 

 t Taylor's Statistics, p. 177. 



