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J, Hall on the Cretaceous Strata of the United States, 83 



la the present state of our knovf ledge, it would appear, that 

 the beds 2 and 3 of the cretaceous formation of Nebraska have 

 gradually increased in thickness and importance in a southwest- 

 erly direction, and at the same time have become more fossiHf- 

 erous. In trachig the same beds through Arlcansas, we find in 

 addition to Inoceramus prohkmaiicus^ cither in beds somewhat 

 higher in the series or associated with that fossil, Ilolectypv^ 

 planatus, Toxaster eteganSy Holaster simplex^ Cardiuvi muliistriatian^ 

 Inoceramus confertim-ann ulatns^ Grypha^a Pitch en] and others 



which occur also among the Boundary collections. These facts 

 clearly show that the beds have become much more fossiliferous 

 ^ than on the Missouri, or on the Kansas and Blue Rivers; and. 



we must regard the greater part of the Boundary collections as 

 derived from the horizon of these beds. 



From the great vertical range of the characteristic cephalo- 

 poda above enumerated in Xew Jersey, and their wide geo- 

 graphical distribution, and from their marked distinction to the 

 types of fossils holding the lower position, we shall probably 

 find it convenient to subdivide the cretaceous formation into 

 three great groups. 



3. The upper division, comprising the first and second marl 



beds of New Jersey, with the intermediate ferruginous sand, 



Ig. and the clay below the first greensand bed; parallel to the beds 



4 and 5 of Nebraska. 



2. The middle division, equivalent to the beds 2 and 3 of 

 Nebraska, the calcareous and higher argillaceous beds of the 



I 



southwest, Arkansas, Texas, and New Mexico, containing many 

 .Echinoderms^ Inoceramus prohlematicus, Oryphcea Piicheri^ Hippu- 

 riteSj Caprina^ Nerinea^ Ammonites Texanus^ and numerous other 

 fossils. 



1. The lower division, represented by No. 1 of the Nebraska 

 s- section, and including the various sandstones and shales or clays 



at the base of the formation in the Llano Estacado, and other 

 portions of New Mexico; and probably equivalent to the lower 

 clay beds of New Jersey, "in which the only fossils yet known 

 are of vegetable origin. 



It is not unlikely that the medial division may prove in many 

 localities to be divisible into distinct beds beyond those recoo-- 

 nized in Nebraska ; or, that as the formation expands to the 

 southward, other beds not known on the Missouri will come in, 

 or that the two there known will be found to become much 

 modified in character. 



species, not known in the ^ame association in New Jersey and Alabama, tnnj occur 

 in connexion with Exogyra codata in the southwest, we cauiiot at this time separate 

 the species belonging to the upper and lower divisions of the ft»rmation. 



I learn also from Dr. Parry, since these pages were written, that he regards the 

 bed containing Exogt/ra cosinta and other species, as holding a higher position than 

 the calcareous beds of Leon Springs, and other localities aloii^ the route. 



