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vicinity of Santo Tomas there is a local exception to the usually uniform 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 escarpment, several hundred feet in height, which has been described under the name "Balcones escarpment." Along its foot is a strip of country

from 6 to 15 miles wide, which is broken by faults and in which there has been considerable volcanic disturbance. This scarp is the southern edge of the vast Edwards Plateau. It is composed of practically horizontal limestone strata, and attains an altitude of some 2,500 feet.

The vegetation consists of grasses, which at the time of our visit were mostly dead and dry, and of a variety of prickly plants belonging "

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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.

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.