BUILDING STONES. 647 



THE FERNANDIAN BLUE MARBLES. 



Trending usually northwest by southeast (magnetic bearing), but occasion- 

 ally involved in later uplifts, there is a set of calcareous beds included in the 

 same system with the hard iron ores, but overlying the latter. In the best 

 exposures of these marbles the iron ores are often buried beneath them, but 

 if the dip be nearly vertical the marbles may appear to lie in belts parallel to 

 the magnetites. 



Usually the Fernandian marbles are blue, highly crystalline, and at sur- 

 face very fragile, but there are some which are exceedingly tough and fine- 

 grained. The color is not usually attractive for most purposes, and contami- 

 nation with spots or thin streaks of pyrite often mars the appearance in cer- 

 tain exposures, but there are some outcrops which give promise of a better 

 product. It is always very difficult to determine the wearing qualities and 

 the solidity of masses of marble which have been exposed for ages to corrod- 

 ing agents from a mere examination of surface indications. Our samples in 

 the State Geological Museum at Austin illustrate different grades of the blue 

 marbles, and some of them taken beneath the weathered capping are firm 

 and uniform in color. Usually they are thin-bedded, and sometimes the 

 fractures, due to successive uplifts, are too numerous to admit of securing 

 large blocks. On account of the dark and dull colors these deposits have not 

 received the attention from prospectors which they really merit, and which 

 they may receive when a demand for marble shall arise in the district. 

 There is some variety in the coloring between the light gray and dark blue. 



As far as can be judged from present developments the best qualities of 

 this class occur in the southern portion of the Central Mineral Region, where 

 they have been rendered more tough by metamorphism, but there are some 

 very promising deposits of greater extent in Llano County, upon Little 

 Llano Creek between Pecan Creek and San Fernando Creek. 



THE TEXIAN WHITE MARBLES. 



There is a limited expression of very excellent white marbles in a few areas 

 where the Texian strata have been favorably situated for metamorphism with- 

 out excessive disturbances. The region about Enchanted Rock and south- 

 ward has produced the best examples thus far, but there is also a tract south 

 and southeast of Packsaddle Mountain which has good exposures. The ver- 

 tical hachures upon the Economic Map indicate the places where there is 

 reasonable chance of discovering outcrops of value. In a portion of the dis- 

 trict outlined northwest of Mason there are signs of similar deposits. Occa- 

 sionally the surface croppings are friable and of buff or brown tints. 



A few of these exposures may be profitably worked whenever transporta- 



