Geographic Features of Texas. — Hill. 13 
region, which is an ancient plain, whose individuality has 
nearly been destroyed in the process of its reduction to mod- 
ern base level, and by the elevation and subsidences which it 
has undergone in post-Tertiary times, of which more will be 
said later on. Within this timbered area there is a great 
diversity of minor topographic and geologic features similar 
to those mentioned in my Arkansas report, which can not be 
described here. The most conspicuous of these are (1) minor 
prairies of late Quaternary origin, and (2) a great deposit of 
gravelly debris extending from Arkansas to the Rio Grande. 
These late Quaternary prairie formations are of two kinds of 
sediments and possibly of two epochs. In north Texas, as at 
New Boston, and in Arkansas, they are composed of sterile 
clay derived from the Ouachita system and are of no agri- 
cultural value. South of the Trinity, extending to the Rio 
Grande, they are known as "black prairies," and are often con- 
founded with the true Black Prairie region, described later, 
for their structure is the debris of the chalky formations of 
the latter, degraded, transported and redeposited in later 
times — one of the numerous examples of redeposition so 
abundant throughout the cotton belt. These prairies are of 
varying extent and distribution. I tentatively consider these 
of later origin than the gravel. The gravel marks the line of 
sea level at the epoch of the deposition of the Plateau Gravel 
of Arkansas, which was early Quaternary, of which it is the 
direct southern continuation, the general trend of that forma- 
tion changing after crossing the Red river, from west 
to west of south, and leaving the mountain system to the 
north. The average altitude of this great gravel deposit is 
from four to five hundred feet, and its widtli seldom exceeds 
fifty miles, yet it extends intermittently from the Ouachita to 
the Rio Grande, and doubtless it will some day be correlated 
with the Mississippi and Maryland deposits of a similar 
nature and the intimate relation of the time of its marine 
deposition to the entirely different, glacial phenomena of the 
northern states, full}^ deciphered. The material of this great 
gravel deposit varies with the character of the formation of 
the interior from which itAvas derived, and has not been trans 
ported from the north. In Arkansas it is clearly the debris of 
the Ouachita system against which it was deposited. In the 
central part of its extent in Texas it is composed of the debris 
