THE COAL-FIELDS. 45 



One can easily conceive the difficulties which these disruptions 

 frequently throw into the miner's way, who, in following what he 

 considers a valuable seam of coal, is suddenly stopped by coming 

 in contact with a fault, and finds the coal shifted several yards 

 above or below, or even completely lost. 



On the other hand they are productive of considerable advan- 

 tages, for by intersecting a large field of coal in all directions, 

 and by the clayey contents which fill up the crack accompany- 

 ing the fault, they become coffer-dams, which prevent the body 

 of water accumulated in one part of the field from flowing into 

 any opening which might be made in it from another. This 

 separation of the coal-field into small areas is also important in 

 case of fire, for in this case the combustion is prevented from 

 spreading widely, and destroying, as it would otherwise do, the 

 whole of the seam ignited. 



6 The natural disposition of coal in detached portions,' says 

 the author of an excellent article in the c Edinburgh Eeview,' * 

 ' is not simply a phenomenon of geology, but it also bears upon 

 national considerations. It is remarkable that this natural dis- 

 position is that which renders the fuel most accessible and most 

 easily mined. Were the coal situated at its normal geological 

 depth, that is, supposing the strata to be all horizontal and un- 

 disturbed or upheaved, it would be far below human reach. 

 Were it deposited continuously in one even superficial layer, it 

 would have been too readily, and therefore too quickly, mined, 

 and all the superior qualities would be wrought out and only 

 the inferior left ; but as it now lies it is broken up by geological 

 disturbances into separate portions, each defined and limited 

 in area, each sufficiently accessible to bring it within man's 

 reach and labour, each manageable by mechanical arrangements, 

 and each capable of gradual excavation without being subject to 

 sudden exhaustion. Selfish plundering is partly prevented by 

 natural barriers, and we are warned against reckless waste by 

 the comparative thinness of coal-seams, as well as by the 

 ever augmenting difficulty of working them at increased depths. 

 By the separation of seams one from another, and by varied 

 intervals of waste sandstones and shales, such a measured rate of 

 mining is necessitated as precludes us from entirely robbing pos- 

 terity of the most valuable mineral fuel, while the fuel itself is 



* Vol. cxi. p. 80. 



