BUILDING MATERIALS. 365 



presented merely as a preliminary report. For practical purposes the best 

 discussion of the subject may be made topically by substances as below: 



1. THE GRANITES. 



To treat this division fully it would be necessary to arrange the granitic 

 rocks of our district into not less than seven or eight distinct types, each 

 characteristic of one particular uplift among those which have been described 

 in Part I of this Report. Commercially there will be as many or more vari- 

 eties whenever the demand has sufficiently stimulated the development of the 

 the resources of this kind in Llano, Burnet, Gillespie, Blanco, and Mason 

 counties, named here in the order of area of exposures, beginning with the 

 largest. 



It would be very difficult now to so describe each one of the granites so 

 clearly that any one could determine by simple inspection which type he is 

 handling. Nor can those who will work them usually make geologic dis- 

 tinctions based upon differences in the modes of occurrence; for the chief 

 criterion — the strike of the mass — is in very many cases only determinable 

 from a knowledge of the texture itself. When numerous quarries are ship- 

 ping the different grades, a commercial classification may be adopted which 

 will not agree closely with the one here proposed, but there is a kind of 

 textural relationship which makes this provisional arrangement at least of 

 temporary value. Adopting then as a basis of affinity the structural charac- 

 ters, using texture, colors, etc., as a means of further division when necessary, 

 we get seven fairly distinct classes, viz. : A, Gneissic Granites ; B, Compressed 

 Granites; C, Block Granites; JD, Friable Granites; JEJ, Mixed Granites; F, Di- 

 mension Granites; G, Fissile Granites. 



Only in a very general way may this be regarded as a scientific grouping, 

 but in proposing it an attempt has been made to get as near to the order of 

 formation, or age, as can well be done without more intimate knowledge of 

 the outcrops than has yet been acquired. 



A. THE GNEISSIC GRANITES. 



These are gneisses and quartzose mica schists in the Archaean exposures, 

 which do not offer any prospect of becoming valuable as building material, 

 unless it may be for restricted and commercially unimportant uses. But, in 

 addition to these, extensive masses of compact, streaked granites, usually 

 fine-grained and sometimes easily workable, occur in the oldest rock systems, 

 especially in Llano County. 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 granite tract 

 between Spring Creek and Clear Creek, it is very probable that excellent 



