460 GEOLOGY OF NORTHWESTERN TEXAS. 



durable. In selecting building stones or a place to open a quarry much in- 

 formation may be obtained by visiting the locality and seeing what effect the 

 weather has had upon the stones exposed to the action of the atmospheric 

 influences. The rocks that are thus exposed have been subject to these influ- 

 ences for thousands of years, and will show what may be expected of the 

 stones when quarried and put into buildings. If the bed of stone is entirely 

 hid from observation by the material of its own destruction it will prove to be 

 a stone that will suffer greatly on exposure, but if it stands out in bold escarp- 

 ment while the other parts of the strata are decomposed, it shows that it has 

 a strong power to resist the atmospheric influences. It must be remembered, 

 however, that the most obdurate material will show some effects of weather- 

 ing; even the hardest granites have been decomposed by the relentless hand 

 of time. 



The color of a stone to be desirable must be uniform and permanent after 

 weathering. Very few stones, if any, will retain the same color as when 

 first quarried, and it is very desirable that there should be no nodules of 

 pyrites that will cause streaks across entire walls below where such a nodule 

 may occur. 



It is always desirable that a stone that is to be used in a large building 

 should be subjected to all the tests that have been adopted for determining 

 these matters, such as the chemical constituents of the stone, its crushing ca- 

 pacity, its power to resist the action of carbonic acid, its ability to absorb 

 moisture, as well as the facility with which it can be dressed under the ham- 

 mer of the workman. 



For testing the crushing weight of a stone cubes should be prepared two 

 inches square, in duplicate, so that its resistance both in the direction of the 

 bedding and in a line across the bedding may be tested. Many stones are 

 much more durable and will stand much more pressure if put into a wall in 

 the same way they were bedded in the quarry than if set up on edge. 



No tests of the stone in this part of the State have been made by the Sur- 

 vey except some very brief and simple tests to determine some of the quali- 

 ties of some of the limestones, and they were not made with a view of deter- 

 mining their value as building material. 



CARBONIFEROUS BUILDING STONE. 



In the Carboniferous formation in Texas, from the bottom to the top of the 

 series, there are beds of excellent building stones, both of sandstones and 

 limestones. Mention is made in the description of the several counties, else- 

 where in this Report, of a number of places where these stones have been 

 brought into use. 



