4 UNITED STATES GEOLOGICAL SUKVEY— TERTIARY FLORA. 



is five thousand feet liiglicr, the distance is five liundred miles, admitting 

 horizontality of the measures and uniformity of the grade, tlie belt of the 

 Cretaceous should occupy about half the width of the i^lain between the 

 Missouri River and the base of the mountains. This estimate is, however, 

 too high; for, along the Missouri River, Dr. Ilayden fixes the eastern limits 

 of the Cretaceous, or the appearance of the Tertiary over them, at Fort 

 Benton;* and considering tlie Lignitic area as marked in his geological map 

 of the Yellowstone and Missouri Rivers.f that of the Cretaceous would, from 

 east to west, be about one-third the width of that of the Tertiary. 



The first record we have of the area of the Lignitic, or at least of its 

 wide extent along the Missouri and the Yellowstone Rivers, is obtained from 

 the narration of the voyage of Lewis and Clarke in 1804. The following 

 passage is copied from R. C. Taylor's Statistics of Coal, p. 174 : — 



"The coal, or lignitic, was first observed twenty miles above the 

 Mandan village. The bluffs on each side of the river are upward of one 

 hundred feet high, composed of sand and clay, with many horizontal strata 

 of carbonated wood, resembling pit-coal, from one to five feet each in thick- 

 ness, and occurring at various elevations above the river. At fifty miles above 

 the village, similar coal seams were noted; bnt here they were observed to be 

 on fire, emitting a quantity of smoke and a strong sulphurous smell. Further 

 on, the same sulphurous coal continued for eighty miles more ; strata of coal, 

 frequently in a state of combustion, appearing in all the exposed faces of the 

 bluffs. The quality of the coal improved as the party advanced, near the 

 mouth of the White River, eighty-five miles farther, aflTording a hot and 

 lasting fire, but emitting very little smoke or flame. Thence forty-seven 

 miles, to the Yellowstone River, and at a bluff eight miles up that stream, 

 were several strata of coal. For fifty miles above the junction of the Yel- 

 lowstone and the Missouri, there were greater appearances of coal than had 

 yet been seen, the seams being in some places six feet thick; and there were 

 also strata of burnt earth, which were always on the same level with those 

 of coal. The explorers had thus far traced this lignite formation along the 

 banks of the Missouri for a distance of three hundred and thirty miles. The 

 horizontal formation of clay, loam, and sand, with fragments of coal in the 

 drift of the river, extended three hundred miles more, to Muscleshell River, 



• Dr. F. V. H.iyden, Annual Ucport, 18G9, p. 48. 



t United Stales War Department Map of thu YellowHtone and Misbouri Eivers, e.xplored by Capt. 

 W. ¥. Raynolda and Lienl. 11. l',, Miiynadier, 1850-60. 



