438 GEOLOGY OF NORTHWESTERN TEXAS. 



Coal Seam No. 7 north of the Clear Fork of the Brazos River lies entirely- 

 above the massive limestone ; while Coal Seam No. 1 lies entirely below all the 

 massive limestone beds. A trained geologist would be able to trace the hori- 

 zon of either of these seams by the accompanying rocks, whether he could 

 see the outcrop or not, and would be able to indicate where a shaft would 

 reach the seam, though it might be at some distance from an outcrop, with 

 reasonable certainty. There are areas in which each of these seams are too 

 thin for practical purposes, but these localities can only be determined by 

 actual experiment. 



In prospecting for coal it is only necessary to drift a few feet on the out- 

 cropping seam, so as to see the seam in its normal condition, away from 

 where it has been subjected to the influences of the atmosphere. A drift of 

 ten feet is generally sufficient to determine the thickness and quality of a coal 

 seam at a given locality. Where there are sufficient outcrops to show the 

 seam in several places in the same vicinity, several such openings should be 

 made, so as to determine the general thickness of the seam and to furnish 

 data for an estimate of the amount of coal a given area would furnish. It 

 is also important that a shaft or drill be put down some distance from the 

 outcrop, that the thickness of the seam may be known in that direction. I 

 prefer a shaft to a drill, for the reason that it is not an easy matter to get a 

 correct report from the driller of the exact strata passed through. Where a 

 drill is depended upon, every piece of the core should be taken out and 

 washed and preserved, and a correct record made of it. There is a general 

 disposition to overestimate the thickness and quality of a coal seam found by 

 boring. No reliability is to be placed upon the work of any kind of drill ex- 

 cept one that brings up a core just as it occurs in the strata. Drop augurs 

 for prospecting purposes are worthless. 



KINDS OF COAL. 



The only kind of coal found in this coal field is what is known as bitu- 

 minous. It is high in volatile matter, and burns with an abundant yellow 

 flame. 



COAL ANALYSIS. 



' The importance of the analysis of coal is to show its value as a heat pro- 

 ducer. It may be said in a general way that the more moisture a coal con- 

 tains the less value it has, because the moisture prevents the combustion 

 and must be driven off: before complete combustion takes place. Part of the 

 heat generated by the other material of the coal must be taken up to drive 

 out this moisture. Again, it takes up a part of the weight that would other- 

 wise be occupied by combustible material. Thus, if a coal has five per cent 



