Extracts relating to Coal, Sfc. 75 



down to find the Coal. If the Coal has no solid strata above 

 and beneath it, but be found only embodied in the clay or 

 other lax matter, it will not be there of its full thickness, nor 

 so hard and pure as in its perfect state when enclosed betwixt 

 two solid stiata, the uppermost called the roof, and the under • 

 most called the 'pavement, of the Coal : in such situation 

 therefore it becomes necessary, either to dig a new pit, or to 

 work a mine forward until the stratum of Coal be found in- 

 cluded betwixt a solid roof and pavement, after which it need 

 not be expected to increase much in its thickness: yet as it 

 goes deeper or farther to the dip, it most likely will improve in 

 its quality ; for that part of the stratum of Coal which Hps near 

 the surface, or only at a small depth, is often debased by a 

 mixture of earth and sundry other impurities washed down 

 from the surf'.ce, through the backs and cutters, by the rains; 

 whilst the other part of the stratum which lies at a greater 

 depth is preserved pure, by ihe other soiid strata above it 

 intercepting- all the mud washed from the surface. 



The above methods of investigation admit of many different 

 cases, according to the greater or less number of favourable 

 circumstances attending each of the modts of inquiry ; and the 

 result accordingly admits every degree of probability, from the 

 most distant, even up to absolute certainty. In some situa- 

 tions, the Coal will be discovered by one method alone, in 

 others, by a comparison of certain circumstances attending 

 each method; whilst in some others, all the circumstances 

 that can be collected only lead to a certain degree of probability. 



In the last case, where the evidence is only probable, it will 

 be more adviseable to proceed in the search by boring a hole 

 through the solid strata (in the manner hereafter described), 

 than by digging or sinking a pit, it being both cheaper and 

 more expeditious; and in every case, which does not amount 

 to an absolute certainty, this operation is necessary to ascer- 

 tain the real existence of the Coal in that place. 



We shall now suppose that, having examined a certain dis- 

 trict, situated within a few miles of the sea or some navigable 

 river, that all ihe circumstances which offer only amount to a 

 probability of the Coal being there, and that boring is neces- 

 sary to ascertain it. We shall therefore describe the operation 

 of boring to the Coal : 



Suppose that a piece of ground, A, B, C, D, has been 

 examined, and from the appearance of the strata where they 

 are visible (as at a precipice and several other places,) they are 

 found to be of those kinds usually connected with Coal, and 

 that the point to which they rise is directly west towards A, 

 but the ground being flat and covered to a considerable depth 

 with earth, &c. the strata cannot be viewed in the low grounds ; 



