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The Azoic age includes the granites and their associated rocks, destitute of fossils, viz : shales, mica schists, gneiss, hornblendes, porphyries, etc., which form most of the mountains in the western part of Burnet county, from which they extend westward through Llano and Mason counties beyond the town of Mason on the Menardville road, about eight miles. The southwestern boundary of these rocks is unknown, but is probably somewhere in Kimball county.

There are two or more periods of the upheaval of the granite in the region under consideration. In the eastern part of Llano county, at and near the Packsaddle mountain, are shales of laurentian age, uplifted at angles near the perpendicular, associated with and on the outer borders of the granite, which are overlaid by nearly or quite horizontal strata of the lower Silurian (Potsdam) to the depth of several hundred feet. In other localities, at Marble Falls on the Colorado, and in Honey Creek cove in Llano county, the limestones and sand rocks of the silurian and carboniferous are uptilted by the underlying granite, at angles of from 25 degrees to 45 degrees and upwards. Still farther west, near Fredericksburg, horizontal strata of the cretaceous, and no other rocks but the cretaceous rest upon the granite.

AZOIC ROCKS WEST OF THE PECOS RIVER.

Fifteen or twenty miles beyond Leon springs, on the road from Fort Stockton to Fort Davis, and a few miles west of Barilla springs, is the eastern border of some azoic rocks, which extend westward to the Rio Grande and into Mexico. In going westward at Barilla springs, at the eastern boundary of the Limpia valley, and on each side of it, are rough and precipitous mountains of dolerite and basaltic rocks. Farther westward, in the Limpia canon, the road is hemmed in on each side by nearly and sometimes perpendicular walls of these rocks, to the height of one thousand feet or more. A few miles to the east of Fort Davis they become feldspathic granites, with little or no mica, and such are most of the mountains around Fort Davis. Col. Andrews, commandant of the fort, told me that one of his officers had seen crystals of mica in that neighborhood, but I did not see any. This mineral is absent or but sparingly disseminated in all the western