1887.] NATURAL SCIENCES OF PHILADELPHIA. 45 



to those of that division as it is known in southern Colorado and 

 New Mexico, but I have recognized several species of fossils as 

 common to the Austin limestone and those more northern strata. 



The paleontological evidence that the Navarro beds are 

 equivalent with the Ripley group of the Mississippi section, as 

 presented by Shumard, ^ seems to be beyond question. It is also 

 known that several molluscan species which characterize the 

 equivalents of the Navarro beds in the Cretaceous of the Gulf 

 and Atlantic coast regions, are not uncommon in the Fox Hills 

 group of the Western section. 



The Fox Hills groups of the Western section is clearly recog- 

 nizable as such in the valley of the Rio Grande, in western 

 Texas, where it is found to contain a number of the characteristic 

 species of the group. The evidence is conclusive, also, that the 

 Fox Hills strata there, are, or originally were, directly continuous 

 with those of that epoch which are found to the northward.^ Of 

 the present, or former, direct stratigraphical continuity of the 

 western Fox Hills strata with their presumed equivalents in 

 Eastern Texas, and in the Gulf and Atlantic coast regions, 

 present evidence is not so clear. 



Although the identity of certain species, found in those 

 eastern and w^estern strata respectively, is beyond reasonable 

 question, there is a decided difference, both paleontological and 

 lithological, between them. Still, there seems to be good reason 

 for regarding them as having been synchronously deposited. 

 Their differences were perhaps largely due to the presence of a 

 land area between an eastern and a western marine area during 

 the Fox Hills-Riijley epoch, to the southward of which the two 

 marine areas coalesced. This view seems to find corroboration 

 in the fact that most of the species which are common to both 

 the eastern and western strata, are open sea forms, and conse- 

 quently had a wdde geographical range. Those species which 

 differ most in the two regions respectively, are apparently such 

 as had a more restricted range. 



We now come to consider the relation of the Fox Hills strata 

 and the Navarro Beds respectively, to overlying formations. It 

 a.ppears to be unquestionable that the Lignite Tertiary Beds of 

 eastern Texas rest directly upon the Navarro Beds, just as the 



1 Proc. Bost. Soc. Nat. Hist., viii, p. 189. 

 ^ This volume, pp. 18-20. 



