REPORT OF THE STATE GEOLOGIST. lxxix 



For the purpose of this discussion, Texas is readily separable into 

 three divisions : 



1. The Gulf Slope, Cenozoic. 



2. The Central Basin, ...... Paleozoic. 



3. The Western Mountain System, .... 



The area covered by the Gulf Slope includes all the region east and 

 south of the western and northern boundary of the Grand Prairie pla- 

 teau, which stretches southward from the Bed River to the Colorado, 

 and thence westward to the Rio Grande. In area this comprises fully 

 one-half of the State and by far the most thickly settled portion. 



The Central Basin includes all that portion of the State west and 

 north of the Grand Prairie, extending to the Gaudalupe Mountains on 

 the west. 



The Western Mountain System covers the remainder of Trans-Pecos 

 Texas. 



The Gulf Slope is in a certain degree a continuation of the topo- 

 graphic and geologic features of the States east of us which border 

 upon the Gulf, but in some ways its differences are as pronounced as 

 its resemblances. Thus, with the exception of a little marshy ground 

 in the southeastern corner there is none along the entire coast. Differ- 

 ences in amount and character of rainfall and of temperature have also 

 resulted in the production of a somewhat different topography, especi- 

 ally toward the Rio Grande, and the soils of certain formations are of 

 far greater fertility than those derived from rocks of similar age in the 

 other States, owing to peculiar conditions of formation. 



The different sediments which now appear covering the surface of 

 this area were laid down by the waters of a great sea, which in its pres- 

 ent restricted basin we call the Gulf of Mexico. 



Beginning at the coast in low and almost level prairies the ascent is 

 gradual towards the interior, in many places not exceeding one foot per 

 mile for the first fifty miles. Through this comparatively level plain, 

 which comprises the exposure of the strata embraced under the general 

 name of "Coast Clays," the streams move sluggishly in tortuous chan- 

 nels, and for the most part through an open prairie country, the only 

 timber being along such water courses and in scattered motts or islands. 

 As we pass inland this is succeeded by other belts which, having been 

 longer subjected to erosion, show a surface more and more undulating 

 as we recede from the Gulf. The ascent is also more rapid, and some 

 elevations of as much as seven hundred feet are found, as at Ghent 



