108 



SINKING FOR COAL. — IRONSTONE. 



gritstone ; we shall then have a model of the coal strata in many 

 parts of England, and their situation over the metalliferous lime, 

 with the beds of sandstone, by v^^hich they are separated from it. 



From the inclination or bending of coal strata, they always rise 

 near to the surface in some parts of their course, and would be visi- 

 ble if not covered by soil or gravel. In the intersections formed 

 by rivulets, or by accidental fractures on the sides of hills in a district, 

 the nature of the strata may often be determined, and should be as- 

 certained before any expense be incurred in boring or sinking for 

 coal. When this is done, a proper station should be chosen ; which 

 requires great judgment ; otherwise it is possible to bore or sink to 

 great depths, and miss a bed of coal which exists very near the place. 

 This will be evident from the inspection of the two stations, a and 5, 

 Plate IV. fig. 2. ; in the latter it would be impossible to meet with the 

 bed of coal, c, because the search is made beyond the line where 

 it rises to the surface, or, in the miner's language, crops out. At «, 

 coal would be found after sinking only a few yards.* In most situa- 

 tions, it is better to search for coal, as deep as can be done without 

 expensive machinery, by sinking a well in preference to boring. By 

 sinking, a decisive knowledge of the nature and thickness of the strata 

 can be ascertained as far as you descend, which can be only imper- 

 fectly known by boring ; for the latter mode is liable to great uncer- 

 tainty of result, from bendings or slips of the strata. If, for instance, 

 the borer be worked in the situation «, Plate IV. fig. 2., it will pass 

 through a great depth of coal, which in reality may not be more than 

 a few inches in thickness. Besides the uncertainty of the results, 

 the grossest impositions are sometimes practised to answer interested 

 purposes, and induce proprietors to continue the search, where there 

 is no reasonable probability of success. Where coal strata come to 

 the surface, they are generally in a soft decomposed slate, and inter- 

 mixed with earthy matter. They frequently present no appearance 

 of coal, but the soil may be observed of a darker colour. The real 

 quality of the coal cannot be ascertained until it is found below, in 

 its natural undecomposed state, -lying between two regular strata of 

 stone or indurated clay. In general it is observed, that the same 

 bed improves in quality, as it sinks deeper into the earth. Coal 

 strata are generally split or divisible into rhomboidal blocks, by ver- 

 tical joints: these are called slines; the oblique shorter joints are 

 called cutters. 



From what will be stated in the subsequent chapter, it will appear 

 that there is more than one third of England in which all search for 

 valuable coal is useless : the knowledge of a negative fact becomes 



* In 1811, 1 saw in Radnorshire, a fruitless search for coal of this kind ; a bed 

 of coal of a bad quality rose near the surface, and the attempts to obtain it were 

 made beyond the outcrop of the bed. 



