MEMBERS OF THE PRESTON SECTION. 305 



ferrugination has produced hard indurations of deep brown sihcious 

 hematite. This induration is superficiaL It will be observed that these 

 beds have three outcrops on the map. Two are small east-and-west strips ; 

 one south of Denison and the other thirty miles northward — five miles 

 south of old fort Washita. The third is a great north-and-south belt 

 west of them and extends from Red river southward to the Brazos. 



The reasons for brief correlation of these beds with the Dakota by 

 Shumard are good, so far as our imperfect knowledge of the poorh'' 

 defined Dakota as a whole will allow. They are of the same lithologic 

 character as the Dakota to the northward in Kansas, and in some of the 

 indurated ironstones I collected the same dicotyledonous fossil plant 

 previously noted by Shumard,^ principall}^ Stercidea, Salix, Populus, 

 etcetera. I have had no time to undertake the critical study, except 

 in a general way, of my collections or the paleontology of these beds, 

 having deferred it until the study of the lower Cretaceous f is completed. 



Eagle Ford Shales. — The Eagle Ford shales of my original section X of 

 the Texas Cretaceous appear lithologically modified along the line of our 

 Denison profile between the south bank of Iron Ore creek at Cooks 

 springs and at Sherman. The continuity of the entire section could 

 not be made out, but I present it as far as I can safely interpret it. 



At the base the beds consist of yellow arenaceous layers and clays, 

 which grade up into dark blue shale similar in color to the Cretaceous 

 shales of Colorado, and not of the marly white colors that distinguish 

 the Comanche clays. In their middle and upper portion there are manj^ 

 blue calcareous concretions, septaria, with beautifully preserved fossils, 

 while they terminate near the top with an arenaceous horizon abound- 

 ing in fish remains, teeth and the unique Ostreo, bellaplicata of Shumard. 

 These clays which underlie prairie regions are undoubtedly Benton. 



Austin Chalk. — The typical Austin chalk surmounts the Eagle Ford 

 shales in the city of Sherman, and is of the same general character as 

 has been previously described in its extent to the southward. The areal 

 outcrop of the formation here forms the highest point of the whole 



*Mr Taff has presented the only detailed stratigraphy of the Dakota and Eagle Ford beds in the 

 region south of Denison to Waco along the south strip, and this portion of his report is a valuable 

 contribution. He does not treat of their extension east of Denison, however. 



t.Vm. Jour. Sci., April, 1887, pp. 288, 289. 



1 1 have always drawn the line between the Eagle Ford and underlying Dakota at the yellow 

 silicious band on the nortii bank of Iron Ore creek near Cooks springs, at the horizon of the asso- 

 ciation of Cyprimera crassa. Meek, not Cragin, and Exogt/ra columbclla. Other species in the Com- 

 manche series are erroneously called by these names in the Texas reports. Cyprimera crassa of 

 Cragin as used in the reports of the Texas survey is not C. crassa of Meek, and the latter only 

 occurs in the Upper Cretaceous and not in the Comanche of Texas. Mr Taff announced in his first 

 report the " first discovery " of Exogyra columhella in Texas in the beds of the Washita in central 

 Texas, although it had been previously reported from this Eagle Ford horizon (see the Texas 

 section of the North American Cretaceous, Am. Jour. Sci., October, 1887, p. 297). In his second 

 report he apparently abandons this reference, and properly mentions it in the Eagle Ford horizon. 



XLH— Bum.. Geol. Soc. Am., Vol. 5, 1893. 



