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



nally across the map, is bordered with many ancient terraces or deposi- 

 tion planes. 



The following features, although secondary to the above, are also of 

 importance : 



The Antlers (Trinity) valley is a low topographic groove extending 

 parallel to the foot of the mountains. It is a valley of headwater erosion. 



The Goodland escarpment, which limits this valley to the southward, 

 forms the northern scarp of the prairie region and is an escarpment of 

 stratification. 



Extensive second bottoms of the streams or benches are found above 

 their present levels. 



The eastern Cross Timbers are erratic belts of timber occupying the 

 upland and confined to the outcrop of certain arenaceous terranes. 



The genesis and relation of these topographic features will be brought 

 out in the course of the geologic discussion. 



Drainage. — The valley of Red river everywhere represents the lowest 

 drainage channel, but there is also an extensive secondary system of 

 drainage coming down from the mountain region on the north and flow- 

 ing southward into Red river. No survey of this has been made in 

 Choctaw Nation, but it is equally diversified there as in the Chicka- 

 saw and Arkansas portion of the area. This drainage is marked by the 

 large proportion of water to the length of the streams and its excessively 

 wide bottoms as we approach the level of Red river. South of Red river 

 an entirely different and probably newer system of secondary drainage 

 is met, flowing directly away from Red river and into the Trinity and 

 the Sulphur. 



Forest Groivth and its Relation to geologic Structure. — One of the most 

 instructive features of this region is the relation of forest growth and 

 prairie to geologic structure, and its bearing upon the southwest term- 

 ination of the great Atlantic timber belt. The rainfall is everywhere 

 here sufficient to produce abundant arborescent growth, as shown by the 

 belts of timber crossing it, but the region is varied by sharply defined 

 prairie and forest areas, the distribution of which is entirely in con- 

 formity with the peculiarities of geologic substructure. 



The prairie regions are of five kinds : 



1. The Prairie d'Ane type. Small open spaces in the heart of the 

 great Atlantic timber belt, surrounded everyw^here by the forest growth 

 of virgin Appalachian flora. These prairies conform in area with the 

 extent of the fresh-water Pleistocene deposits of the Prairie d'Ane type, 

 namely, prairie d'Ane, prairie de Roan, and Bois d'Arc prairie of Arkan- 

 sas, and New Boston prairie of Texas. They are usually surrounded 

 by a growth of liquidamber. 



