640 CENTRAL MINERAL REGION OF TEXAS. 



herent weakness of such granitic rocks, it need not be taken as a necessary 

 disqualification of the type as a building stone. All over the region of the 

 disintegrated material there is an abundance of tough knolls of apparently 

 equivalent rock, which has escaped degradation, although subjected to similar 

 conditions for ages. So, in hills and mountains like the Spring Creek ridges 

 in Burnet County and the Cat Mountains in Llano County, there are massive 

 outcrops worn into mounds and fantastic forms, the whole exhibiting both 

 the weakness and the strength of this class of granites in different portions of 

 the mass. By judicious selection of the indurated parts and those which 

 have acquired attractive tints by oxidation there may be developed a gigantic 

 industry. One advantage of the working of such fields is that a variety of 

 such granite is liable to be at command, for it is usually in places where later 

 outbursts have occurred that the representatives of this class are hardened 

 enough to thus resist denudation. 



There are some varieties of speckled granite, having the minute flakes of 

 black or white mica scattered through a compact base, which merit special 

 consideration. These vary much in character, shading into binary granite 

 without mica upon the one hand, and upon the other into streaked, banded, 

 and laminated gneiss. A few in Gillespie and Blanco counties, and others in 

 Llano and Burnet counties, are particularly noteworthy. Many of these might 

 readily be overlooked by a casual observer, but the skilled collectors of the 

 Geological Survey have added not a few to the Museum collections. These 

 are not to be depended upon, as a rule, for great quantity in any one locality, 

 nor can it be expected that uniformity will show through large masses; but 

 this lack is fully offset by the enhanced value of the local outcrops in conse- 

 quence. 



Too much disturbance may, in some cases, have resulted in cracks and flaws 

 which will unfit these granites for use in large blocks. But, as stated in 1889. 

 page 365: 



If the best of these can be quarried in places where they have been least disturbed by 

 more recent uplifts, as in parts of the Babyhead region, and perhaps also in the Burnet 

 County tract between Spring Creek and Clear Creek, it is probable that excellent speckled 

 and mottled varieties may be obtained. These will frequently polish with good effect, and 

 some outcrops show by their style of weathering that certain oxidation tints of value for 

 ornamentation may be utilized. In working this class, however, great care will be necessary 

 to select only those qualities in which the mica is well distributed and in comparatively fine 

 scales. Otherwise serious blemishes may result from irregularity of "weathering." Eor 

 paving blocks, foundation stones, and special uses much of this material may be utilized 

 eventually at little cost. 



These remarks apply with equal force to a large area in northeastern Ma- 

 son County, which I have examined in detail only within the last few months. 

 In Llano County there is a very fine-grained red -speckled gneiss of this va- 



