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granites which came under our notice, with the exception of that east of Isleta.

About twenty miles west of Fort Davis, near the El Paso road, are several mountains of white quartz, so white that in the distance they resemble mountains covered with snow. Some of these are 7000 feet or more high.

At Muerto springs, westward a few miles further, quartoze and feldspathic veins are common, forming whitish lines up the sides of the mountains.

About thirty miles further west, at Van Horn's well, the prevailing rocks are dolerites and basalts, dark colored and massive. Twelve miles further west, are feldspathic granites intersected by large veins of quartz and feldspar of the orthoclase form. Hornblende rocks are also here. At Eagle springs, the mountains are similar as regards their rocks, to those at Fort Davis. Ten or twelve miles east of the Rio Grande, near the El Paso road, north side, one of the highest mountains is called Blanco, from its white appearance, caused by its quartz rocks. These mountains abound in quartoze veins. Twelve to fourteen miles east of Fort Quitman, is a group of mountains of igneous origin, which I did not visit.

About a mile above Hart's mill, on the Rio Grande, and four miles above El Paso, there is a mass of quartoze granite, the quartz placed so regularly as to resemble porphyry. This granite has a few small specks of mica, and is an excellent building rock. It rises but a few feet above high water mark on the river, and is overlaid by carboniferous and cretaceous rocks.

About thirty miles east of Isleta, is a group of granite mountains of two or three hundred acres area rising from 300 to 500 feet above the plain; these are called Cerro Hueco. These mountains are naked or nearly naked granite, and isolated from all other rocks. These granites contain but a small proportion of mica. From two to three miles further east, are the Sierra Alta mountains, of a height of more than 6000 feet composed mostly of limestones. On the western side and near the base of one of these mountains, there is a large dike of feldspathic granite, about forty feet thick dipping at an angle of about forty-five degrees beneath limestones of carboniferous age.

Going southward into Presidio county, below Fort Quitman on the south, to and in the vicinity of the Hot springs,