I;. T. HILL — THE TEXAS-NEW MEXICAN REGION. 01 



Southern Pacific railway to Del Rio, the directions of the portions mentioned of 

 both of these roads being controlled entirely by it. To this eastern escarpment of 

 the Kerrville plateau the Mexicans have applied the appropriate name "Balcones." 



The northern border of the Edwards plateau is marked by the southern wall of 

 the Colorado canyon from Austin to Travis peak as an irregular escarpment of erosion 

 running westward through San Marcos and McCullough, forming the boundary of 

 the Llano-Mason Paleozoic area. It turns westward and southwestward through 

 Concho and southern Tom Green counties, and thence irregularly forms the breaks 

 of the Concho river ; and it merges with the Llano Estacado in Howard, Martin. 

 Tom Green and Midland counties. It is a true escarpment of erosion. 



An examination of the map will show that the Edwards plateau proper east of 

 the Pecos occupies many thousand square miles, including most of the counties of 

 Pecos, Edwards, Crockett, Schleicher, Yal Verde, and Bandera and about one-half 

 of the counties of Kinney, Uvalde, Bexar, formal. Hays. Concho. Tom Green, 

 [Hon, Upton and Crane, and a small portion of Travis. In Upton and Midland 

 counties the rocky surface of the plateau In ■comes the prevalent floor of the peculiar 

 Llano Estacado formation which extends thence northward. Its narrowest width 

 is found along the 32d parallel ; after crossing this narrow neck, about fifty miles 

 in width, the western escarpment is reached, forming the eastern breaks of the 

 Pecos valley, and continues southward along that stream forming a valley from 

 500 to i.iiim) feet deep to the Rio Grande. In fact, the Edwards plateau is hut the 

 southern continuation of the floor of the great Llano Estacado plateau, the same depo- 

 sition level from which the Llano Estacado formation has been mostly eroded. 



The greater part of the summit of the Edwards plateau, like the Llano Estacado, 

 is void of streams. Its eastern margin is indented by a number of streams, which 

 are the most beautiful in the state of Texas* These streams usually have enormous 

 canyons in proportion to their volume. They are mostly mountainous toward their 

 headwaters, but near the point of emergence from the Balcones escarpment they 

 How through their own debris in canyons and valleys vastly out of proportion to 

 their present volume, which no doubt represent the ancient sea level of the Rio 

 < irande embaynient. 



It will he well to observe that there are no sharp topographic or structural bar- 

 riers between the I'M wards plateau and I he Llano Estacado. ami that any difference 

 between them is in the surface formation and due to the greater erosion of the 

 eastern border. Taken together they constitute a single vasl mesa 500 miles long 



and 280 miles wide, surrounded on all sides by escarpments, all of which have their 

 origin in the underground water of this vast mesa. While composed of the same 

 strata as the northern extension of the < irand prairie, the Kerrville plateau, topo- 

 graphically and genetically, should be considered a portion of the Llano Estacado. 

 Another interesting tact of the Edwards plateau is the series of ancient volcanic 

 necks along its southeastern margin, from Austin to Del Rio, to which I have pre- 

 viously given the name of Shumard knobs. 



The Led, Brazos and Colorado and also the Rio < irande have cut deep into and 

 in places entirely through the formation of the Grand prairie (the Comanche series 

 and their valleys present the same atmospheric terracing as the western border. In 

 places these river valleys assume the a -pert of vertical canyons, as in the ( loloradoi 

 I'ecosand Rio Grande. The depth of these valleys In-low the level of the plain 

 increases southwestward from 200 to 700 feet. 



The degradation which the northern borders of the Edwards plateau and its 



