COPPER. 



579 



regions. Knowledge of these structural features enabled the writer to pre- 

 dict with some confidence, in speaking of the future of a mining shaft in Gil- 

 lespie County, that "there is a possibility that deeper working may strike 

 similar schists to those in the earlier trends in the Babyhead district," etc.* 

 This has been verified by the discovery in this shaft, early in the year 1890, 

 of copper-stained schists identical with those farther north. Test borings 

 with the diamond drill now in progress under the direction of Mr. G-. C. Gage 

 on Pecan Creek, Llano County, show similar complications in the structure. 



THE NORTHERN OR LLANO-SAN SABA BELT. 



The cut (Fig. 62) illustrates the general character of the surface conditions 

 as shown in an actual section instrumentally taken from the boundary line 

 between Llano and San Saba counties, southward down the valley of Pecan 

 Creek nearly to Cottonwood Creek. In this section the Burnetian schists 

 are cut directly on the dip, but the other systems cross the line of section 

 obliquely and can not be drawn so as to represent the real dip. 



Fig. 62. 



Section through the Northern Copper Field, along the upper valley of Pecan Creek, Llano 

 County. Taken along line A-B, on map (Plate XXI). 



The copper ores occur in regular veins filling small crevices in the gneissic 

 rocks and their associates, and these are best developed as mineral bearers in 

 the axis of a main uplift, or at points where later trends cross the belt. Much 

 of the gneissic material is so highly impregnated with malachite (green copper 

 carbonate) as to give it a rich green color which masks the real character of 



*Loc. cat., p. 331. 



