NATURAL SCIENCES OP PHILADELPHIA. 118 



nes3, and is probably a ridge left after the denudation of the Cretaceous strata 

 previous to the deposition of the Tertiary. Neither the Cretaceous beds, 

 uor the Tertiary that overlie them, exhibit in this vicinity any evidences of 

 upheaval. The Cretaceous strata here have an extent of only about eight 

 miles, and arc exposed only along the banks cut by the river, yet in that space 

 they reveal the remains of marine mollusca in a profusion which I have seen 

 in no other locality. The whole thickness exposed on the Yellow Stone does 

 not exceed twenty-five feet above the water level, and the distant hills on 

 either side are composed of Tertiary beds. At this locality the fossils show a 

 complete blending of this and the succeeding bed, in the ascending series. 



We will now return to White or Smoking Earth river below Fort Pierre, and 

 trace this formation into the interior of tliat interesting region. Passing up the 

 valley of White river, we find it occupying the country bordering upon that stream 

 for about fifty miles above its mouth. Near this point outliers of the White river 

 Tertiary Basin begin to cover the highland, and No. 4 is seen along the river 

 for about twenty miles farther, when it is concealed by Tertiary strata. The 

 intervening country east and north east of the Bad Lands to the Shyenne river. 

 a distance of one hundred and fifty miles, is for the most part underlaid by 

 this bed, except an extension of Fox Ridge, to the sources of the Teton river, 

 which is composed of Formation No. 5 of the Vertical Section. The extensive 

 area drained by the Shyenne river is composed of No. 4, excepting tlie sources 

 of a few of its tributaries. Sage and Bear' creeks take their rise in the "White 

 river Tertiary Basin, but flow mostly through this Formation, revealing large 

 quantities of Cretaceous fossils. A few small tributaries have their origin in 

 the Fox Ridge, and Cherry river has its source in the Lignite Tertiary Basin, 

 near the head waters of the Little Missouri. 



lu summing up the extent of country underlaid by this great formation, we 

 find that south of the Lignite Basin, it occupies an area of two hundred 

 miles in length and one hundred in breath, or twenty thousand square miles. 

 North of the Great Lignite Basin, commencing at its first appearance near Milk 

 river, we find it covering an area of two hundred miles in length and sixty in 

 breadth, or about twelve thousand square miles. I have been thus particular 

 in estimating its approximate limits and extent of surface on account of its 

 influence on the future destiny of that region. Wherever this deposit prevails 

 it renders the country more completely sterile than any other geological 

 formation I have seen in the nortli-west. We see from the above estimate 

 that it renders barren over thirty thousand square miles of the valley of the 

 Missouri. 



The fossils of this formation are too numerous to mention in detail. The 

 upper and lower members appear to be exceedingly fossiliferous, while the 

 intervening portions of considerable thickness contain only a few imperfect 

 ,specimens of Cephalopoda and the bones oi Mosasatirus missouriensis. The entire 

 thickness of this formation may be estimated at about three hundred and fifty 

 feet. 



Formation No. 5 of Vertical Section. 



This very interesting bed, though diff'ering lithologicallj' from the preceding 

 one, contains many of the same species of fossils. It is worthy, however, of a 

 distinct position in the series, not only from its extent, thickness and difference 

 of composition, but also from the more favorable influence that it exerts upon 

 the country underlaid by it. In ascending the Missouri river it first makes its 

 appearance near the mouth of Grand river, about one hundred and fifty miles 

 above Fort Pierre. Near Butte aux Gres it becomes quite conspicuous, acquir- 

 ing a thiclcness of eighty or one hundred feet, and containing great quantities 

 of organic remains. Here it forms an extension of what is called Fox Ridge, 

 a series of high hills having a northeast and southwest course, crossing the 

 Missouri river into Minnesota at this point. Its north eastern limits I have 

 not ascertained. In its south western extension it continues for a considerable 

 distance nearly parallel with the Missour' osses the Moreau river about 



1857.] 



