78 /. Hall on the Cretaceous Strata of the United States. 



or Alabama, and appear to be restricted to these beds. At the 

 same time the species identical with, or analogous to species of 

 New Jersey and Alabama occur in beds Nos. 4 and 5, which 

 may be regarded as subdivisions of one group. 



We are warranted therefore in referring tne beds above Ko* 

 3, to the age of the fossiliferous beds of New Jersey and Ala- 

 in -which the specimens occur brought by Capt. Fremont from the Smoky Hill river, 

 and by Capt. Stansbury from between the Big and Little Blue rivers. 



Dr. Hayden has likewise made extensive collections in other parts of the Nebraska 

 Cretaceous and Tertiary formations during the past two years. The new species of 

 these collections have been deficribed by Messrs. Meek and Hayden in several papers 



Published in the Proceedings of the Academy of Natural Sciences of Philadelphia, 

 hese explorations, with the extensive collections of fossils, have served to fcu^^tain 

 the correctness of the order of succession among the subordinate members of the 

 series, as given in the section above, indicating however that the beds Nos. 2 and 3, 

 as well as Nos. 4 and 5, may in some localities merge into each other ; wliile the 

 limits between Nos. 3 and 4 remain well marked throughout the region explored.^ 



A careful comparison ot Inoceramus fragilis, fro^ibed No. 2, Nebraska Section 

 (Hall and Meek, Memoirs Amer. Acad., vol v, new series, page 388) has satisfied 

 both Mr. Meek and myself^ that it is identical with L problcwaiicus, the specimen 

 described being the young of that species. The young specimens of the latter shell 

 from Arkansas and Smoky Hiil river present no essential difTerences from those of 

 Nebraska. 



* From the fact that Mr. NicoUet remarks (page 36) that the part of stratum A. 

 above water on the day of hia "examination was tliree feet," we may infer that the 

 sandstone No. 1, was not seen by him. 



In this section, Nos. 2 and 3 correspond to A and B of Mr. 

 Nicollet's section; wliile tlie sandstone No. 1 was either over- 

 looked bj him or may have been referred to the Carboniferous 

 strata,"^ 



The division C and D, Mr. Nicollet's section, are subdivisions 

 of Nos. 4 and 5, of our section, or probably of No. 4 alonCj since 

 No. 5 is not known to occur on that part of the Missouri which 

 was examined by Mr. Nicollet. Although admitting of several 

 subdivisions from changes in lithological character, the beds of 

 No. 4 do not present any groups of fossil species restricted within 

 the physical or lithological limits designated, and they can there- 

 fore scarcely be regarded as of importance in the classification 

 of the formation, or valuable in tracing the limits of its members 

 over a w*ide extent of country. 



The subdivisions A and B corresponding to Nos. 2 and 3 of 

 our section, are more important ; and although yielding so few 

 fossils on the Missouri they become well marked in other parts ^ 



of the country. The ^ ^ Inoceramns BarahinV'^ represented by Mr, 

 Nicollet as found in great numbers at Dixon's Bluff, " very much || 



compressed and so arranged as to give the rock a slaty structure," 

 is undoubtedly the Inoceramus prohlematicus which is known to 

 occur in this position and does not occur in the higher beds of 

 the formation upon the Missouri, so far as known at the present 

 time. The Ostrea congesta^ and all the other fossils from beds 

 Nos. 2 and 3, of the section, are unlike species from New Jersey 



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