6 UNITED STATES GEOLOGICAL SURVEY— TERTIARY FLORA. 



of the area of the Lignitic in the map of his Statistics of Coal, 1848.* As 

 an introduction to it, he remarks (p. 23) on that enormous range of brown 

 coal, apparently of the Tertiary period, which follows the eastern flank of 

 the Rocky Mountains, from near Mexico even to the Polar Sea: — " Nature", he 

 says, "has indeed worked on a truly gigantic scale. We see here a deposit of 

 brown coal so extensive that the magnitude of its proportions is far from 

 being defined ; yet enough is known to show that it exceeds in longitudinal 

 range and breadth all others of the present surface of our planet. So far 

 seems to be established, that, allowing li])erally for interruptions in continuity, 

 supposing that any such exist, it occupies thirty-five degrees of latitude, or 

 near two thousand five hundred miles, following the oblique range, and has a 

 maximum breadth on north latitude 48° of four hundred miles; the whole 

 area, as near as we can venture to compute, being two hundred and fifty thou- 

 sand square miles, or one hundred and sixty millions of acres, more than 

 twice the size of Great Britain. Compared with this, the largest coal-fields 

 in the world are absolutely small." 



Audubon and Harris ascended the Missouri to the mouth of the Yel- 

 lowstone River. In the account of their voyage, they give, on thd Tertiary 

 strata of the country, details in accordance with those recorded by Lewis and 

 Clarke.f The whole series of strata, for many hundred miles prior to reach- 

 ing this formation, is described as perfectly horizontal; the upper part of each 

 bed or rock being successively intersected by the angle of descent to the 

 river. The Tertiary group is indicated by the remarkable strata which form 

 the picturesque hills noticed by travelers, and called Mauvaises-Terres by the 

 trappers and voyageurs. Mr. Plarris counted in one place eight seams of coal 

 between the river bank and the top of the bluff, varying from six inches to 

 four feet in thickness. This coal, he observes, is very light, and ignites with 

 difficulty, emitting a very unpleasant odor while burning. Fossilized wood 

 is very abundant, occasionally much flattened by the pressure of overlying 

 strata. Mr. Bell was the only one of the party who had an opportunity of 

 witnessing the burning of the cliffs about thirty miles above the Yellowstone, 

 on the northern bank of the Missouri, and all agree in attributing their burning 

 to the spontaneous combustion of the coal. Mr. Harris states that tlie coal- 

 seams commence in the upper part of Nicollet's great Cretaceous clay bed, 



* Chart showing the imsition of thu coal-fields ou the surface of the k'"^**; ^y Kichard Taylor. 



♦ Proceedings of the Academy of Natural Sciences of Philadelphia, May, 184.5. 



