14 
RIO GRANDE COAL FIELDS OP TEXAS. 
[BULL. 164, 
vicinit}^ of Santo Toroas there is a local exception to the usually uni- 
form direction of dip of the strata. Here the dip, instead of being to 
the southeast, is to the northeast, according to information furnished 
by Mr. D. D. Davis, superintendent of the Cannel Coal Company's 
mine. This disturbance is, without doubt, genetically connected with 
the uplift of the Sierra Santa Rosa of Mexico. 
The northern limit of this plain is a great southward-facing escarp- 
ment, several hundred feet in height, which has been described ' under 
the name " Balcones escarpment." Along its foot is a strip of country 
Fig. 1. — Map showing the general position of the Rio Grande coal fields. 
from 6 to 15 miles wide, which is broken by faults and in which there 
has been considerable volcanic disturbance. This scarp is the south- 
ern edge of the vast Edwards Plateau. It is composed of practically 
horizontal limestone strata, and attains an altitude of some 2,500 feet. 2 
The vegetation consists of grasses, which at the time of our visit 
were mostly dead and dry, and of a variety of prickly plants belong- 
1 R. T. Hill: Am. Geologist, Vol. V, No. 1, Jan., 1890, pp. 17-18; Am. Jour. Sci., 3d series, 1887, Vol. XXXIV, 
pp. 291 et seq. 
2 The geographic features of the region are more fully described in a paper by Mr. Hill and the 
writer entitled The Geology of the Edwards Plateau and Rio Grande Plain: Eighteenth Ann. Rept. 
U. S. Geol. Survey, Part II, 1898, pp. 193-323. 
