652 CENTRAL MINERAL REGION OP TEXAS. 



County), there is not much outside of the Cambrian System. Much of this 

 last is friable or nonresistent from weak cementation, but there are localities 

 near the later granitic outbursts where very durable sand rock can be quar- 

 ried, some of it of attractive appearance. The localities which give most 

 promise are along the southern border, near Enchanted Rock, Gillespie 

 County, in the neighborhood of the Dragon Fangs, and southward on Little 

 Bluff and Bluff creeks, in Mason County. The white and buff hardened sand- 

 stones or fine conglomerates of the Lower Cambrian, as on House, Putnam, 

 and Packsaddle mountains, may be used with good effect, and they can be 

 readily obtained in quantity of large dimensions, some of the beds being from 

 ten feet to twenty feet thick. There are special situations where the Cam- 

 brian red sandstones have been hardened by semi-metamorphism, but in 

 many cases they are not sufficiently indurated to be serviceable in construc- 

 tion. Often they are highly calcareous, as is shown by the white incrusta- 

 tions left upon surfaces of erosion along the creek beds. This is a very com- 

 mon effect at the north end of the Riley Mountains, in Llano County. 



Some of the hardened sandstones or incipient schists of the Texian System 

 which abound in southeastern Llano County and in much of the adjoining 

 region south of Packsaddle Mountain, as well as in the vicinity of Lockhart 

 Mountain, and to some extent north of Mason, in Mason County, may be 

 utilized as building stone, by careful selection. The chief objection to this 

 material is its broken up condition, but this is not always the case. 



E. SLATES, SCHISTS, ETC. 



There have been no severe tests of material supposed to be adaptable as 

 roofing slate, and yet the outcrops of such rocks are numerous and easily 

 worked. It is difficult now to say whether the Burnetian, Fernandian, and 

 Texian strata include good material of this class, because the essential ele- 

 ments of durability can only be proven by actual practical use. But in places 

 where the Texian and Fernandian have been hardened by the action of im- 

 prisoned heat, many exposures occur of strata of suitable color and tough- 

 ness. Big Sandy Creek, southeast of Packsaddle Mountain, courses for 

 miles through this class of rock. Similar conditions prevail in other regions, 

 as in a portion of the area east of Enchanted Rock. The best districts, how- 

 ever, so far as can be judged from the outcrops, are east of the Riley Moun- 

 tains and along the valleys of Comanche and Beaver creeks, in Mason County. 

 These are the Texian fields par excellence. 



The Fernandian and Burnetian schists at surface are rarely slaty; the 

 Texian rocks incline to the block structure, but the chances for discovery of 

 suitable roofing slate are much better among the last named rocks than with 

 the others, which are usually brittle or granular; or if tough they do not com- 



