314 E. T. HILL — GEOLOGY OP RED RIVEB. 



counties, thus adding to the difficulty of differentiating the unconsoli- 

 dated clay formations in a prairie country covered by a thick residual 

 soil, but wherever the chalky rocks occur they again become evident. 

 As we go westward, however, into Grayson county, where the more con- 

 solidated beds enter into the structure, the faults become tangible and 

 play a potential part in the topographic features, as explained on a 

 previous page. Still north in the Chickasaw Nation, near Carriage 

 point, intense faulting with the same northwest strike can be seen in the 

 Eagle Ford prairies. 



Mr Taff has recently described an important fault (the Cooks springs 

 fault) south of Red river and parallel to the Preston fault, in which, 

 however, the downthrow is reversed, being to the southwestward. 



Near Roxton and Ladonia, in the southeast corner of Lamar county, 

 the northwest and southeast faults (presumably of the Red river system) 

 are visible. 



Between Clarksville and Anona, in Red River county, the northeast 

 and southwest faulting is seen in the upper chalk of the Glauconitic 

 division. In the line of the great Balcones system it will be seen by 

 projecting the strike of these two fault systems upon the map of Texas 

 that the small county of Rockwell lies very near to where they cross 

 each other. This county takes its name from a peculiar sandstone dike, 

 previously described, which projects through the clays near the base of 

 the Glauconitic division. The southeastern or Red river system of fault- 

 ing will explain the remarkable change of strike which takes place at the 

 west end of our map. In the Chickasaw nation and northwest Grayson 

 county a kind of wedge is formed by the opposite downthrows of the 

 Preston and the Cooks springs fault, which projects northwestward into 

 an angular ridge. Probably several faults of this whole system have not 

 been exactly located, for all of the Chickasaw nation north of Red river 

 has certainly dropped far below the level of the opposite country in 

 Grayson county, Texas. The age of this faulting is not clear, but it could 

 not have been much earlier than the time of the PJateau gravel, probably 

 during the Neocene. 



Variation of Sedimentation away from the Ouachita Shoreline. 



The various beds of the whole section do not all strike away from the 

 Ouachita shoreline in the same direction over the Texas region. The 

 second bottoming occurs in all the river's southward at least as far as the 

 Colorado, probably beyond, and extends farther inland in places than 

 the Plateau gravel. The Plateau gravel shoreline, as I have previously 

 published, continues to occupy the divides as far southwest as Austin, 



