DESCRIPTIVE GEOLOGY. 685 



the sandstone is scarcely in sight. Occasionally we find in view the sand- 

 stones along the Mosquez Canyon on the road to Alpine. As far as the ore 

 bearing is concerned, it will be probably confined to the outer portions and 

 foothills or where the igneous rocks are in contact with the limestones; the 

 parts where the lavas and kindred rocks prevail are not promising to pros- 

 pectors. 



As far as slightly reconnoitering discloses, the vesicular lavas extend 

 through the Chispa Mountains towards the Viejo and Capote mountains down 

 the Chinatti range. They are also found between Marfa and the Chinatti 

 Mountains, where numerous agates and onyx veins are contained in the coarse 

 vesicular lava. 



In the tributary water courses of the Cibolo Creek south of the Saocito 

 and below Humphries' sheep camp, glassy lava, resembling opalized wood and 

 retinite, cover many square miles and extend in many places to and into the 

 Chinatti Mountains, where granitic, trachytic, and metamorphic rocks alter- 

 nate with each other. The ores prevailing in the Chinatti Mountains in their 

 southern portion on the east and west slopes seem to be lead ores with vary- 

 ing quantities of silver, mostly also containing bismuth and frequently anti- 

 mony. On the eastern slope free milling ores seem to prevail ; on the western 

 slope lead sulphides and carbonates with silver and bismuth. 



The examination of the Chinatti Mountains was not carried far enough to 

 lead to any but the general conclusion that the Chinatti Mountains must be 

 regarded as eminently ore bearing in those places where the plutonic, eruptive, 

 lime, and other metamorphic rocks are in contact; that, however, the volcanic 

 portions where the lavas, basalts, and trachytic rocks prevail can not be 

 recommended so well to prospectors, though it is claimed that gold was found 

 in the vicinity of trachytic rock. 



I did not have the time to pay closer attention to the Sierra Capote and 

 the Viejo Mountains, but judging from the trip I made in 1886 across the 

 Yiejo Pass I suppose that the basaltic and other volcanic rocks predominate 

 in that portion of Trans-Pecos Texas, and that in all probability they are sec- 

 ond in value to the Chinatti prospects and the Quitman and the Carrizo 

 mountains, as far as ore bearing is concerned. The Sierra Bofecilios and 

 Refugio, east of Presidio del Norte, are very rough and rugged. Trachytic 

 rock rests on a yellowish sandstone, and the formation at least very much re- 

 sembles that of the Limpia Mountains near Fort Davis; but to the present 

 time I have not had the time for the necessary analytical and microscopical 

 work to confirm this supposition. No prospecting was done in the Bofecilios 

 and Refugio, but float pieces of strongly ferruginous quartz and iron, not less 

 iron stained and decomposed leads which can be traced not infrequently for 



