DENISON REDS AND THEIR FAUNAS. 329 



Fort Worth and Cleburne, but at some point not yet determined between 

 the latter place and the Brazos its color becomes lost. The paleontologic 

 horizons, however, continue southward under the lithologic aspect of the 

 Fort Worth limestone, constituting at Austin the few feet of marly clays 

 with G. pitcheri between the zones of Ammonites leonensis and Kingena 

 wacoensis, which form the upper beds of the Fort Worth limestone there. 



Fossils of the Marietta Beds. 



Leiocidaris liemigranous, Shumard. Gryphxa pitcheri^ Morton. 



^Ophioglypha texana, Clark. Ostrea carinata, Lamarck. 



^Oervillospis invaginata, White. Trigonia emoryi, Conrad. 



*Ostrea qu,adnplicata, Shumard. Plicahda dentonensis, Cragin. 

 fStefirnsia rohhinsii, White. 



Without break the brown Marietta clays grade upward into the North 

 Denison sands — beds characterized by alternations of excessively ferru- 

 ginous, laminated sands and clay, which by infiltration and induration 

 are sometimes converted into a fossiliferous hematite. The hematite 

 strata are often of great hardness and are excessively fossiliferous. The 

 sands of these beds could easilv be and have been confused with the 

 Dakota sands of the Soutli Denison, but their distinct stratigraphic 

 position is beyond question. 



The fossils are abundant and beautifully preserved, both as shells and 

 moulds. The species are mostly littoral mollusks not occurring in the 

 lower beds, such as Axinea, NacaLr.a, Corbula, Tapes^ Tarritella, etcetera, 

 which coincide with their physical composition in the testimony that 

 these beds are more littoral than others of the Washita division, and are 

 indeed its shallowest, most littoral deposits. 



The typical occurrence of these beds is in the northern half of the city 

 of Denison. They reappear along an east-and-west strike in Indian 

 Territory, from east of Marietta eastward to the Missouri, Kansas and 

 Texas railroad. 



It is interesting to note that the outcrop of these sands is occupied by 

 the same kind of forests as the Dakota sands of South Denison in their 

 narrow extent along the western border of the lower Cross Timbers, so 

 tliat the areal extent of the lower Cross Timbers can no longer be said to 

 be exactly coincident with the Dakota, but it includes in its western por- 

 tion a very narrow strip of the Lower Cretaceous. 



The sandy ferruginous beds are not sharply differentiated from the 

 overlying and underlying beds, either paleontologically or stratigraph- 



* Has not been seen by the writer south of Tarrant county, 

 t Occurs in Exogyra arietina beds at Austin. Rare. 



XTjV— Rur.r. riKor, Sor. Am., Vor,. 5. 18^. 



