Geographic Features of Texas. — Hill. 19 
coincident with the Balcones. These have partially been 
described in previous papers ; the most conspicuous exam- 
ples are old Fort Inge, near the present town of Uvalde, and 
Pilot Knob, south of Austin. The dikes reported at Rock- 
wall, some two hundred miles north of the last mentioned 
locality, and the peridotite outcrops of Pike county, Arkansas, 
recently described by Branner, are directly in the trend of the 
disturbance. A more intimate connection will no doubt be 
shown when the intervening region is explored. For these 
hills I have proposed the name of Shumard Knobs, in honor 
of the brothers, G. G. and Dr. B. F. Shumard, the first state 
geologists. These knobs and their origin will be discussed 
later in a paper by Mr. Dumble and the writer. 
The Grand Prairie. 
This conspicuous plain lies immediately west of the Black 
Prairie region and extends across the state parallel with it. 
After crossing the lower Cross Timber, as the valley which 
accompanies the base of the White Rock scarp is termed, or 
ascending the ^scarp of the Balcones south of Austin, the 
extensive plateau of this region is reached. As shown on the 
map it extends across the geographic center of the state in 
irregular outline from the Ouachita mountains, north of Red 
river, against which it abuts, to the Trans-Pecos and Mexican 
mountains, which have uplifted and destroyed its southern 
end. Its eastern margin is regular, coinciding with the west- 
ern margin of the Black Prairie just described. The western 
border, however, is more irregular and broken in outline. 
Lake the Black Prairie this region is almost divided by 
destructive erosion of the Colorado into two conspicuous 
areas, north and south of that stream. The northern area is 
the elongated plateau lying between and elevated above the 
two vallays of the upper and lower Cross Timbers, as seen 
between Fort Worth and Weatherford, Waco and DeLeon, 
ijainesville and Henrietta, or along the line of any other 
transecting railway. The southern portion is similar in gen- 
eral asi)ects and structure, except that it is Avider and deflects 
westward into the truly arid region. Although a very unique 
area in Texas, there is no local name given to this southern 
division, except that universal and meaningless term "the 
mountains," which is applied to its eastern and western mar- 
gins — the Balcones and buttes respectively. Nine-tenths of 
