374 CENTRAL MINERAL REGION OF TEXAS. 



Sands for concrete of various tints may be readily obtained at surface in 

 many places. For the most part these are very pure, and no doubt other 

 uses will be found for them whenever the demand arises. Red sands from 

 the waste of the Cambrian sandstones are especially prevalent. Hematite 

 sandstones have already been referred to in the discussion of the iron ores. 

 The decay of these has produced in many cases extrusive tracts of brilliant 

 red sands, some of which are noticed beyond under the head of "Materials 

 for Paints." 



VII. REFRACTORY MATERIALS. 



Many of the rocks referred to under the head of building stones may be 

 applied in situations where great heat is required, and there are besides not 

 a few other kinds which will resist high temperatures. Probably the acidic 

 schists may often be so employed to advantage, and in cases demanding such 

 materials the tough basic slates and schists are al! that can be desired. 



The Cambrian and Silurian rocks are not suitable for such uses as a rule, 

 but the Pre-Cambrian exposures are readily accessible and widely distributed. 

 It is only necessary in this place to notice a few specially important sub- 

 stances, which may hereafter have more than a local value. 



I. SOAPSTONE. 



I have not yet seen any steatitic rocks which give promise of becoming 

 important except as fire-proof substances, although some of the talcs and 

 soapstones are pure and free from grit. They are almost invariably foliated 

 to such an extent as to prevent their application in other ways, unless in the 

 powdered condition. So far as now known the talcose rocks are confined to 

 the Burnetan System, although their absence from the Fernandan outcrops is 

 not certainly proved. They may occur in other trends than the earliest 

 (north 75 degrees west), but as yet none are known to belong to any of the 

 later systems. One of the best exposures is about two miles south of west 

 from the Smoothing Iron Mountain, in the valley of San Fernando Creek, in 

 Llano County. 



This has a semblance of foliation, but it may be sawed or cut into blocks 

 and slabs with a smooth exterior. As a lining for furnaces and for other pur- 

 poses not demanding a decidedly firm texture, the material is excellent. 

 Some care may be necessary in the selection to prevent flaking or exfoliation, 

 but the rock is superior to much that has been marketed and used with 

 apparent satisfaction. Most of it is not pure white. Grey is as nearly a 

 description of its tint as can be given in one word. Sometimes there is a 

 speckled or marbled appearance upon freshly cut surfaces. The quantity is 

 great enough to supply a large industry, and careful search along the strike 



