R. T. Hill—Cross Timbers in Northern Texas. 295 
Indian Territory into Northern and Central Texas, and im- 
mediately adjoining the foregoing topographical division on 
the west. Its western border follows a line drawn through 
Dallas and Austin, from Denison to San Antonio, where it 
makes a western deflection to the Rio Grande. Geologically, 
this region is also a continuation of the features of the other 
Gulf States, but beyond its western edge the continuity ceases. 
It differs from the Coastal Plain in being at a much greater alti- 
tude, and consisting almost entirely of a level prairie region. 
Its altitude is from 450 to 750 feet. 
Third.—VYhe Central Denuded or Hilly Region. This area, in 
itself, embraces a great nuinber of unique and well-marked 
topographic features, each of which is worthy of a more detailed 
description than can be here given. It might be called the 
‘butte ” region, the ‘“drouth” region, or by any of a dozen local 
descriptive names equally ‘applicable to it; but its general fea- 
tures are all the result of one great cause, an excessive amount 
of superficial denudation. It includes all the country west of 
the Black Prairie Region to the escarpment of the plains, in the 
northwest, and to the T'rans-Pecos mountainous region of the 
southwest. It embraces a multitude of geologic formations, 
but there is in it little* or no evidence of local disturbance in 
thestrata. Its altitude is generally between 750 and 2000 feet. 
Fourth—The Plateau, or Pan Handle Region. This com- 
prises the northern and most extensive half of the Llano Hsta- 
eado, and is a southern continuation of the great plains of 
Kansas. 
Fifth—The Mountainous or Trans-Pecos Region. Most of 
the country west of the Pecos consists of highly disturbed, 
mountainous areas. The general direction of the axes of the 
disturbances is parallel with the course of the Pecos, the Rio 
Bravo, and the Sabinas river in Mexico, all which flow nearly 
due southeast. The eastern border of this area crosses the Rio 
Grande west of the Pecos, continues in Mexico for a distance, 
but again crosses the Rio Grande eighteen miles west of Hagle 
Pass, and for a hundred and fifty miles it extends along the 
Texas side of that river to below Laredo, where it again crosses 
it into Mexico. 
Ihave endeavored to delineate this classification of the 
topographic features upon the accompanying map, plate VI. 
The two belts of the Cross Timbers are entirely within the 
third, or Central Denuded Region, the eastern border of the lower 
timbers coinciding almost exactly with the western border of 
the second topographical area.. The chief geologic agency in 
modifying the surface of this region, as before stated, has been 
subaerial erosion. The only elevation apparent is that which 
* No recorded disturbance ,I should say. There is an important dislocation of 
strata in this region to which I shall soon call attention. 
Am. Jour. Sci.—THIRD SERIES, VoL. XXXIII, No. 196.—APRIL, 188%. 
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