BUILDING MATERIALS. 371 



These are the so-called "Burnet Marbles." Really tney are not true mar- 

 bles. Very beautiful pink, white, buff, blue, and grey varieties may be ob- 

 tained from these beds, and in some cases, especially in McCulloch and San 

 Saba counties, the variegated marbles are somewhat abundant. In some 

 places the strata are thin, but in others slabs and blocks of considerable size 

 may be taken out. The rock is tough, often having a semi-conchoidal frac- 

 ture, and it dresses well, sometimes admitting of a high polish. Upon the 

 whole, there seems to be a reasonable basis for a profitable industry in the 

 utilization of this class of material. 



Some other beds, especially the saccharoidal and birdseye types, may here- 

 after become serviceable as pseudo-marbles, but no attempt has been made 

 thus far to use them. Their outcrops are northward upon Cold Creek, for 

 the most part in San Saba and Burnet counties. 



3. THE COMMON DOLOMTTES. 



There are very few simple limestones in the Central Region among the 

 Pre-Carboniferous rocks, to which our present review is limited. Nearly all 

 the calcareous rocks are dolomytic, excepting some tufas and calcareous sand- 

 stones of little value. The Cambrian dolomytes may occasionally serve useful 

 purposes as material for fences, buried foundations, and bridge piers, for 

 many of them are durable enough, and they can often be obtained in con- 

 venient sizes; but their sombre hues and uneven weathering unfit them 

 for employment in the better class of buildings. Exceptions may be found, 

 but the statement is very generally applicable. The Silurian Beds afford a 

 wider variety, but being dolomytic, and thus weathering black or brown, 

 much care is necessary in selecting them. A good rule is to reject those 

 which are unsightly in old natural exposures, however attractive they may 

 be upon fresh fractured surfaces. Some of the yellow dolomytes of the basal 

 Silurian may, perhaps, be effectively used as trimmings, or even as regular 

 building material, and it may be possible to select other beds from among 

 those which are most even and attractive in natural exposures. There is 

 nothing except the marbles already described which will be liable to command 

 an outside market, although local requirements may sometimes be met to ad- 

 vantage by such supplies of the kind as the district affords. 



The Devonian dolomytes are unsuited for construction. 



4. THE QUARTZITES AND SANDSTONES. 



There are some altered sandstones or quartzites which may become useful 

 where they can be quarried in sufficient quantities or in blocks of suitable 

 size. As a rule these are of ancient origin. They do not occur so regularly 

 or of such uniform character that a general statement as to their distribution 



