44 PROCEEDINGS OF THE ACADEMY OF [1887. 



northward, but there seems also to be a clear line of demarkation 

 between that series and the upper one, within the State of Texas. 

 No unconformity of the strata of the upper series upon those of 

 the latter has yet been satisfactorily observed, but it can hardly be 

 doubted that there is at least a brief chronological break between 

 the two series. This latter question, however, I am not now 

 prepared to discuss. 



From the foregoing remarks it Avill be seen that it is the forma- 

 tions of the upper series alone which can now be discussed with 

 reference to equivalency with the formations represented by the 

 other sections of the foregoing table. Beginning with the lowest 

 member of the upper, or Gulf series, namely, the Timber Creek 

 beds, I regard those strata as, at least in pai't, equivalent with the 

 Dakota group of the Western and ujDper Missouri sections, and 

 perhaps equivalent with the Eutaw group of the Mississippi 

 section. Of the latter supposed equivalency I have no paleonto- 

 logical evidence; and the suggestion is made mainly in conse- 

 quence of the stratigraphical position of the Eutaw group. 



That the Timber Creek beds are equivalent with the Dakota 

 group is indicated not only by the position of each with refer- 

 ence to overlying formations, but I have recognized some of the 

 species which were first found in the Dakota strata of central 

 Kansas, in the Timber Creek beds of Denton County, Texas. 



The Eagle Ford shales are recognized as equivalent with the 

 bluish shales, or lower portion of the Colorado group as it is 

 known in Colorado and the adjoining territories. That is, I have 

 recognized certain of the species of the Eagle Ford shales as 

 identical with some which occur in the Colorado group to the 

 northwestward of Texas. The lithological character of the shales 

 of both regions is also similar. 



As to the equivalency of the Eagle Ford shales with the 

 Tombigbee sand of the Mississippi section, the only reason 

 I now have for offering that suggestion is its stratigraphical 

 position. 



That the Austin limestone is equivalent, both stratigraphically 

 and paleontologically, with the rotten limestone of the Missis- 

 sippi section, as has been shown by other authors, there seems to 

 be no reason to doubt. I also regard those Texan strata as 

 equivalent Avith the upper division of the Colorado group. The 

 Texan strata are not only quite similar in lithological character 



