Geographic Features of Texas. — Hill. 23 
the black Prairie, while the eroded and scarped western edge 
is rapidly receding eastward. That it once covered continu- 
ously the next region to be described is evident, the present 
extent representing about one-half its former extent. 
The next and most conspicuous plain of Texas is the .Staked 
Plains. Before it can be properly described, however, it is 
necessary to consider a great depressed area, which, except at 
its southeast corner, everywhere intervenes between it and the 
Grand Prairie. 
The Central Denuded Region. 
In a brief article published in the American, Journal of 
Science for April, 1887, the writer included all the vast region 
of the northern half of Texas, lying between the eastwardly 
receding White Rock scarp and the westwardly receding scarp 
of the Staked Plains under the generic term of the Central 
Denuded or Butte region, since all the included topography 
(except that of the Grand Prairie, which in this paper is 
removed from the classification) is the result of erosion accom- 
panying the recession of these scarps. This classification, 
being more structural than topographic, however, can only be 
used temporarily for present convenience.' The area em- 
braces great diversit}^ of geologic substructure, mostly of pre- 
Cretaceous age accompanied by a variety of topography, which 
may be provisionally divided as follows : {\) The Old Rock 
regions, embracing (a) the Palo Pinto or Coal country, and 
(b) the Llano, or Marble, Granite and Iron country; and (2) 
The Red Beds, including (a) the Abilene country, and (b) 
the Gypsum country. 
Viewed from any point upon the scarps of the Grand Prairie or 
Staked Plains which surround it, this region is seen to occupy 
what is apparently a depression from 500 to 1,000 feet below 
them and extending from the 98th to the 101st meridians, 
north of the 32nd parallel, into southern Kansas. 
The older rock portion occupies the eastern third of tlie 
region, while the more extensive Red beds occupy the remain- 
der. 
Older Rock Regions. 
From the margin of the Grand Prairie the extent of the 
lower, more rugged, and timber-covered areas of the central 
'This Central Denuded region is an illustration of an ancient anti- 
clinal elevation, which has been reduced to a depression by subsequent 
erosion. (See Part ii). 
