310 R. T. HILL — GEOLOGY OF RED RIVER. 



ROCKPORT SECTION. 



Still eastward the Glauconitic is overlapped, and we find the Eocene 

 covering all, the Tertiary resting directly upon the upturned mountain 

 floor at old Rockport, near Malvern. 



Extent and topographic Expression of the Terranes. 



The basement Trinity sands indicate the most important epoch in all 

 post-Paleozoic history, and, like the movement at the close of the Car- 

 boniferous, may be said to be one of the grand criterial events of our 

 whole geologic history. It represents the baseleveling and invasion of 

 the Texas-Mexican region by the Atlantic, and is the most marked un- 

 conformity in the Texas region. The sands are deposited in southern 

 Indian Territory directly upon the previously baseleveled floor of the 



Figure 1. — Vertical Structure of Paleozoic rocks underlying Prairie west of Ardmore. 



Paleozoic rocks of the southern border of the Ouachita mountain system, 

 as shown in the Arkansas sections. The planing of these Paleozoic 

 folds, upon which the Trinity sands are deposited, took place largely by 

 land erosion before their deposition, for in the Chickasaw nation, west 

 of Ardmore, similar baseleveling is now going on, and the level prairie is 

 composed of the same vertical, planed-off Paleozoic structure as that 

 buried beneath the Trinity sands in Arkansas, as shown in the profiles. 



These sands in Indian Territory and Arkansas now outcrop in a de- 

 nuded valley of stratification, as distinguished from a normal drainage 

 valley ; that is, a valley is formed by the southward receding from the 

 mountains of the escarpment of the Goodland limestone of the Freder- 

 icksburg division. This valley results from the interception of the 

 headwater ramifications of the secondary branches of the main drainage 

 channels. 



West of Marietta, Chickasaw nation, the strike of the whole Cretaceous 

 system turns directly southward through Texas. The underlying floor 



