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 MasoB 

 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 moun- 

 tain, are shales of laurentian age, uplifted at angles near 

 the perpendicular, associated with and on the outer bor- 

 ders 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 Mar- 

 ble Falls on the Colorado, and in Honey Creek cove in 

 Llano county, the limestones and sand rocks of the silu- 

 rian and carboniferous are uptilted by the underlying 

 granite, at angles of from 25 degrees to 45 degrees and up- 

 wards. Still farther west, near Fredericksburg, horizontal 

 strata of the cretaceous, and no other rocks but the creta- 

 ceous rest upon the granite. 



AZOIC ROCKS WEST OF TI^E PECOS EIVEK. 



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 some- 

 times 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 



