R. T. HILL — THE TEXAS-NEW MEXICAN REGION. 85 



The next paper was — 



NOTES ON THE TEXAS-NEW MEXICAN REGION. 

 BY ROBERT T. HILL. 



< 'onti nls. 



Introductory page 85 



The Baton-Las Vegas Plateau 8G 



The Llano Estacado 87 



The Edwards Plateau no 



The Washington Prairies 92 



The Rio Grande Bmbayment 93 



Basin Deposits of the Trans-Pecos Region 95 



1 haracter of the Basins 95 



The Hueeo-Organ Basin 95 



The Mesilla Basin. im, 



The Jornado del Muerto Basin 97 



The Eagle Plats Basin '.17 



Valley of the Salt Lake Basin !i7 



Basin of Mimbrea 98 



Probable Basins of the Peeos Valley 98 



The Volcanic Areas of eastern New Mexico 98 



Introductory. 



The present paper is intended to call attention to certain widely distributed 

 features of the western Texan and eastern New Mexican region not hitherto de- 

 scribed. The region treated embraces 1 he country west of the longitude and south 

 of the latitude of the Ouachita mountains (approximately corresponding with the 

 thirty-fourth parallel). The features discussed are mostly non-mountainous, and of 

 later age (Neocene) than the latest mountain uplifts. 



I have previously shown that the salient topographic features of the region con- 

 sist of: 



1. A series of modern and ancient coast and dip plains,* comprising strata ex- 

 tending from the ( lomanche to recent in age, which cover the eastern half of the 

 state, and collectively forming what maj be called the coastward incline. This 

 embraces the coast prairies (Pleistocene), the Washington prairies (Neocene), the 

 Eolignitic or forest region ( Eocene), the main black prairie (upper < !retaceous),the 

 Grand prairie (Comanche or lower Cretaceous), and the two Cross-Timbers (bases 

 of the upper and lower Cretaceous respectively). The Llano Estacado may be in 

 some respects classified with the coastward incline, hut for the present it may be 

 treated separately. 



■_'. The central denuded region, including the denuded area now occupied by the 



great rock sheets of the Paleozoic and early MesOZOic ( Led beds) of central Texas. 



mostly dipping westward, which lie unconformably beneath the group of the coast- 

 ward incline and the Llano Estacado, and are exposed by their removal through 



erosion 



* Professor W . VI. Davis has objected to the use ol this term (Bull. 1 1. Soc. Am., vol. 2, L890, p. 



>7 1 and substitutes the term "structure plain " I nasi 1 inch as there maj be many kinds of structure 

 plains, of which u dip plain is a specific kind, I continue the use of the term clip plain in preference 

 to the g< neric one proposed by him. 



