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there are many large dikes of basaltic rocks, some of which extend across the Rio Grande into Mexico.

The Chinati mountains, in the southwest part of Presidio county, are chiefly igneous rocks, granites, dolerites, etc.

On the road from Presidio to Fort Davis, about forty miles south of the latter, are low hills of dolerite and basaltic rocks.

All the igneous rocks that we saw north of the Pecos are either of upper cretaceous or tertiary age, shown by the uptilted strata of the cretaceous rocks amid and bordering the mountains. The Cerro Hueco mountains may be an exception. I saw no tertiary fossils beyond the Pecos.

About four miles east of Fort Clark, in Kinney county, on the San Antonio road, are dolerite and basaltic rocks, extending fifteen to twenty rods along the road, and covering much of the hill over which the road passes.

Again, about two miles west of the Nueces, on the same road, there is a similar outcrop.

On the west bank of the Frio at the ford, there is a large mass of basaltic rocks about fifty feet high, extending several hundred feet up the river. On the eastward from the Frio, I saw dolerite rocks in the road and near it quite often. At one place, about four miles eastward from the river, there is a mass of dolerite covering several acres, surrounded by cretaceous limestones.

Again, Pilot Knob, about ten miles southwest of Austin, is dolerite, and here these rocks extend three or more miles, also surrounded by cretaceous limestones.

There are probably other localities of these rocks along the southern borders of the cretaceous region of the State.

The rocks of the lower silurian in Burnet and Llano counties have been noticed in previous reports. To define them correctly, a detailed survey is needed.

In the northwest part of Llano county, about two miles southwest of Smoothing Iron mountain, is a mountain with a sandstone base and limestone top, all of lower silurian; the sandstone below of the Potsdam period, the