K. T. DUMBLE-THE SOILS OF TEXAS. 
31 
The belt of country lying between the Tertiaries and the coast is but 
lately emerged, and its continuation may easily be traced beneath the 
waters of the Gulf of Mexico. The materials are principally clays and 
sandy clays, witli intercalated beds and lenses of sand. During the time 
of their deposition the waters were busy all over the State, and lakes 
and streams abounded everywhere, in which were gathered the pebbles 
and gravel with their coverings of drift materials which are so abundant 
over the entire State. Among the greater of these lakes was that which 
occupied the site of what is now the Seymour plateau. 
The broader features of the distribution of these formations is indicated 
on the accompanying map. First, along the coast is a narrow strip of 
Pleistocene deposits, then a broader belt of Tertiary, followed by the 
wide expanse of the Cretaceous. In the center, a comparatively small 
area of the older rocks, while to the north and west lie the Carboniferous 
and the Permian, crossed by a line of Cretaceous running east and west, 
and by another of Pleistocene extending north and south. Finally, the 
Tertiary of the Llano Estacado, with its fringe of Triassic. The forma¬ 
tions west of the Pecos are not delineated. 
Physical Geography. 
A study of the physical geography of the State shows that the broader 
divisions are: 
The Gulf Slope. 
The Central Basin Region. 
The Mountain Systems. 
The Gulf Slope extends from the Gulf shore to the western and north¬ 
ern border of the Cretaceous highlands. Beginning in a slope so gentle 
that the rise of the level ground is inappreciable, the Coast Prairies spread 
inland over the Pleistocene belt a distance of 50 to 100 miles, and merge 
gradually into the undulating country of the upper Tertiary. Continu¬ 
ing towards the interior, the surface becomes more rolling, and by its 
varied topograph}' evidences the varying beds of sand and clay of the 
Tertiary belt or plain. This is followed by the rolling slope of the Upper 
Cretaceous comprising the famous Black Prairie region, and finally by 
the broad expanse of Lower Cretaceous materials forming what is known 
as the Grand Prairie. On the east this is simply a continuation of the 
geneial slope, but westward it forms a broad elevated plateau. 
West and northwest of the Grand Prairie lies the Central Basin region, 
the Carboniferous rocks of which have for the most part been exposed by 
the denudation of the Cretaceous and later formations which formerly 
overlaid them. The two principal bodies of later material which have so 
far escaped entire erosion are the Seymour plateau and the Llano Esta- 
