68 The American Geologist. Feb. i89o 
CLASSIFICATION AND ORIGIN OF THE CHIEF GEOGRAPHIC 
FEATURES OF THE TEXAS REGION. 
By ROBT. T. Hill, Austiu, Texas. 
II. 
THE VALLEYS OF EROSION.* 
The drainage accompanying the elevation of every plain is 
a record of its decay and destruction. In a previous paper I 
have classified the drainage systems of the Texas region into 
four great classes : (1). Those rivers which rise in the Rocky 
mountains and traverse the whole system of topographic 
plains, such as the Arkansas and the Rio Grande, with their 
principle tributaries, the Canadian and Pecos. (2). Those 
which rise in the eastern border of the Staked plain and which 
are gradually destroying it by headwater erosion, including the 
Red, Brazos and Colorado. (3). Those which rise in the nat- 
ural springs along the great Balcones fracture, and (4) the 
tidal and incipient drainage of the coastal prairies and Eo- 
Lignitic region. The drainage topography of each river sys- 
tem is diif'erent in each ■plain., and resulting therefrom is a 
diversity of basins and valleys, only the chief features of 
which will be mentioned, leaving to others and future investi- 
tion the more detailed interpretation. 
In addition to the valleys clearly attributable to the present 
drainage, there are more ancient and extensive grooves, which 
are radically different, and in some cases probably antecedent 
to the present streams, and which can not be interpreted by 
them. The most conspicuous of these ancient features are : 
(1). The great valley of the Canadian through the Staked 
plain. (2). The trans-Pecos basins. (3). The older valley 
of Red river. (4). The Plateau gravel depression of south- 
west Arkansas. (5). The older terraced valleys of the Grand 
Prairie and coastward regions. 
The Older Valley of the Canadian. 
The Staked plain is no doubt a remnant of the great plains 
of eastern Colorado, Kansas and Nebraska, but it has long 
since been separated therefrom geographically by a great val- 
ley of erosion, which for convenience I here termed the Older 
valley of the Canadian. It is in the topography and structure 
of this and similar valleys that we must look for the history 
of the plain. 
*See the illustrative map of Texas in the January uumber of the Geologist. 
