NATUBAL SCIENCES OF PHILADELPHIA. 115 



la their lithological characters these deposits differ very materially from 

 those of the two succeeding basins, being composed of Avhitish clays and 

 calcareous and siliceous marls and grits, and entirely destitute, so far as 

 known, of any vegetable remains, except very rare fragments of silicified wood. 

 It is chiefly remarkable as being a vast deposit in which were entombed im- 

 mense numbers of Mammalian and Chelonian animals, for the beauty and 

 perfection with which their bones have been preserved, and its unique scenery. 

 The few Molluscous fossils which have been found, show most conclusively its 

 purely fresh water origin, being confined to the genera Ilclix, I'lanorbis, 

 Limnea, c^-c. We have also at this time very conclusive evidence that it belongs 

 to the Miocene age.* 



The main body of the Bad Lands of White river covers an area of about one 

 hundred miles in length and fifty to sixty in breadth, and it is that portion 

 chiefly which is represented on the map. We have satisfactory evidence, 

 however, from its outliers, that it once occupied a very much larger area, and 

 that it has been removed by denudation. In the section it is represented 

 l)y Big Ox and Medicine Hills, these localities revealing the only indications 

 of it along the Missouri river. We have also evidence of its existence to a 

 greater or less extent throughout the valley of the Running Water, also that it 

 covers large portions of the country bordering upon the Platte, especially on 

 its North Fork, and a much larger space might be colored on the map, but we 

 have preferred to let it represent what is now known with considerable pre- 

 cision, and wait for the results of future labors to render our knowledge more 

 complete. 



Basin 2nd. — Great Lignite Deposit. 



This basin occupies a more extensive geographical area on the Missouri than 

 that of the other two united. It has been known since the expedition of 

 Lewis and Clark that a vast formation existed on the Upper Missouri, con- 

 taining Lignite, &c. Information of a like nature has been published by 

 former explorers since that time, but without details of its lithological cha- 

 racters or collection of its fossils that would enable us to determine its age or 

 extent. The collections of fossils now obtained show most conclusively that it 

 possesses the mixed character of a fresh water and estuary deposit, and that it 

 cannot be older than the Miocene period. It is composed mostly of clays, sands, 

 sandstone and lignites, and has already yielded numerous animal as well as 

 vegetable fossils of great perfection and beauty. It is chiefly remarkable, 

 however, for the evidence that it reveals to us of the variety and luxuriance of 

 the flora of that period. In this respect it differs more especially from the 

 other two deposits. 



The extent of country known to be occupied by this basin I have estimated 

 at four hundred miles in length and one hundred and fifty in width, or about 

 sixty thousand square miles. We thus come to an approximate idea of the 

 immense area occupied by this formation, though I am satisfied that when 

 it is thoroughly studied it will be found that the above estimate is much too 

 low. 



Basin 3rd. — Bad Lands of ike Judith. 



This exceedingly interesting deposit occupies a depression in a sandstone 

 formation which rises to the water level at the mouth of Little Rocky Mountain 

 creek from beneath the well-known Cretaceous bed No. 4 of the Vertical Sec- 

 tion. It presents perhaps the most rugged scenery on the Missouri river, the 

 denudation and erosion having been much greater than at the Bad Lands of 



* See a paper by Prof. Leidy in the Proceedings of the Academy for March, 1857, also 

 the succeeding paper by F. B. Meek and F. V. Hayden, in this number of the Proceed- 

 ings. 



1857.] 



