NATURAL SCIENCES OP PHILADELPHIA. 119 



the general geology of the country, its soil, scenery, &c., was likewise given to 

 the public by Prof. Hall, in an interesting paper read before the American 

 Association for the Advancement of Science, at the Providence meeting. 



Subsequent to all these expeditions, one of the writers* again visited Ne- 

 braska, and spent two years in traversing various portions of that country ; part of 

 which time he was aided by Col. A. J. Vaughan, Indian agent, and afterwards 

 by Mr. Alexander Culbertson, and other gentlemen of the American Fur Com- 

 pany. During this expedition he explored the Missouri to the vicinity of Fort 

 Benton, and the Yellow Stone to the mouth of Big Horn River. Also consider- 

 able portions of the Bad Lands of White river, and other districts not immedi- 

 ately bordering on the Missouri. The vertebrate remains collected by him, as 

 may be seen by reference to the various papers by Prof. Leidy in the Proceed- 

 ings of the Academy, embrace a larger number of species than all those previ- 

 ously known from that country, many of which belong to new and remarka- 

 ble genera. Large collections of mollusca were also obtained from the Creta- 

 ceous and Tertiary formations, and have since been published by us, together 

 with remarks on the general geology of the country, in a series of papers in the 

 Proceedings of the Academy Nat. Sc. Phila. Vol. viii. 



Again, in 1856, the same one of the writers returned to that country in con- 

 nection with a government expedition under the direction of Lieut. G. K. War- 

 ren. The new Cretaceous and Tertiary invertebrate remains, together with the 

 new facts in regard to the geology of the country, collected by this expedition, 

 form the basis of this paper. 



Up to the publication of our first paper, about fifty-six new species of 

 Cretaceous and Tertiary mollusca had been published from Nebraska, by Drs. 

 Morton, Owen, Evans and Shumard, and by Prof. Hall and one of the writers. 

 Since that time, sixteen additional new species have been published by Drs. 

 Evans and Shumard, making in all seventy-two species hitherto published by 

 others from that country. Our own investigations (including those here described) 

 have made known one hundred and fifty new species, and two new genera, 

 many of the former of which also belong to types not hitherto recognized in 

 this country. Of these one hundred and fifty species, fifty-four (if we include 

 the Judith River, freshwater and estuary species) belong to the Tertiary system, 

 and ninety-six to the Cretaceous. Fifty of the Tertiary species belong to fresh 

 water and land types, and four to genera inhabiting salt and brackish waters ; 

 being about four-fifths of all the land and freshwater Tertiary species hitherto 

 made known from American formations. The geological position, and vertical 

 range of all our new species, and several of those published by others from the 

 north-west, as well as a number of the well known and widely distributed forms 

 such as Scaphites Conradi, Ammonites lobatvs, A. placenta, Nautilus Dekayi, In- 

 oceramiis problemaiicus, Mosasaurus Missotiriensis,f ^c.,have been determined with 

 considerable accuracy ; so that we have now the means of tracing out the 

 parallelism between these deposits and their equivalents in other countries. 



In a general vertical section of the Nebraska formations given in a paper com- 

 municated by us to the Academy in November last, it will be remembered, we 

 represented the White river Tertiary formations as on a parallel with the Eocene, 

 or oldest member of that system. In doing this we merely followed the pub- 

 lished views of others, without intending to give it as the expression of an 

 opinion based on any of our own investigations : as all the organic remains yet 

 found in that basin, with the exception of a few freshwater shells described by 



* Dr. Hayden. 



tin a section of the Nebraska formntions accompanying the last paper communicated 

 by us to the Academy, we gave as the position in which the remains of Mosasnurus occur 

 in the north west, the upper part of No. 5. This was in consequence of erroneoui 

 infonnanon in regard to the locality from which the specimens given to the Prince of Neu 

 Wied were obtained. The locality (at the Great Bend of Missouri) has since been visited 

 by one of us, and many specimens obtained ; they occupy a horizon about the middle 

 of No. 4 of the section. 



1857.] 



