granites wMch 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 

 Tvhitish 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 orthdplase 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 Blapco, 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 ex- 

 cellent building rock. Tt 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 gran- 

 ite, and isolated from all other rocks. These granites 

 contain bat 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 lime- 

 stones. On the western side and near the base of one of 

 these mountains, there is a large dike of feldspathic gran- 

 ite, 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 Quit- 

 man on the south, to and in the vicinity of the Hot springs, 



