MINERALS. 711 



Granite. 



The principal component materials of the northern part of the Quit- 

 man Mountains are fine and coarse-grained, red and gray, chloritic, syen- 

 itic and ferruginous granites, granite with garnet and graphite, talcose 

 granite (Protogine), Pegmatite, and G-ranulite. They are also found 

 with the crystalline schists of the Sierra Carrizo, in the Chinatti range 

 and further east in the Chicos and Corazones Mountains, the eastern part 

 of the Davis, and the southern end of the Comanche Mountains. The 

 mountain ranges in the northern portion of Trans-Pecos Texas are also 

 partly granitic. 



Porphyries and porphyritic rocks, such as Argylophyre, Melaphyre, Olygo- 

 pyre, porphyritic trachytes, and trachytic porphyries form part of the 

 Quitman Mountains. Extending east to the Sierra Blanca, they reappear 

 near Eagle Flat, and are found in the Davis, Eagle, Van Horn, and the 

 more eastern and northern mountain ranges of Trans-Pecos Texas. 



Mica Schists prevail in the Carrizo Mountains, extending to the Van Horn 

 range, but in the Quitman and other ranges they are sparsely dissemi- 

 nated. Talcose, chloritic, and hornblende schists also prevail in the 

 Carrizo Mountains. 



Mica (isinglass) in larger flakes is found in the western spur of the Van 

 Horn Mountains, near the Rattlesnake (mica) tank. 



Feldspar is found in a number of species in those parts of West Texas 

 which were mentioned with the granites. 



Marbles are found of a dark gray coarse-grained variety on the east and 

 west sides of the Quitman Mountains, while those in the foothills of the 

 Sierra Diabolo are lighter gray and finer grain. There are also marbles 

 found of yellow and peach blossom shades, streaked, and mottled, very 

 fine-grained white and pink, white and purple, and numerous other shades. 



Calcites and aragonites are frequently found in leads and outcrops through- 

 out the metamorphic limestones. 



Volcanic "Rocks are represented by lava, compact and cavernous, basalt, 

 basaltic wacke, obsidian, retinite, and trachytic rocks in the Quitman, 

 Sierra Carrizo, Eagle, Van Horn, and Davis, Viejo, and Chinatti Moun- 

 tains, and probably at least as dykes in the Guadaloupe, Franklin, and the 

 mountain ranges not yet examined. 



Serpentine of brown, oil green, brick red, and also mottled (serpentinous 

 marbles) exist as dykes, and flank the same mountains in the foothills of 

 the Sierra Diabolo. 



Iron. 



Siliceous magnetite and hematites occur in the Quitman, the foot hills 

 of the Sierra Diabolo, Sierra Carrizo, and Chinatti Mountains, 



