COAL. 57 



the roof is of sandstone or shale supported on stout pillars of coal. It is 

 also to be remembered that the further a level is driven into the hill side, 

 the greater will be the depth of superincumbent rock, and consequently 

 the greater the expense for stronger timbering to withstand the increased 

 pressure. 



On the other hand, should the above difficulties not prove insur- 

 mountable, the coal could be mined, for a considerable time at least, by- 

 levels driven into the hill sides from the out-crops of the seams. The 

 advantages of this would be important. The preliminary cost of shaft- 

 sinking through unproductive rock would be saved, and also the expense 

 of winding-gear to raise the coal, including the capital sunk in machinery, 

 and the consumption of coal for winding-engines, such as are necessary 

 in mines worked by shafts. The coal need merely be run out to the 

 surface on tramways laid along the main levels. Further, pumping 

 machinery and engine-power therefor, which form an important item of 

 expense in shaft mines, would not be required, as the mines would drain 

 themselves. The soft, friable state of the coal, and the high dips, would 

 lead one to expect a considerable percolation of water from the surface. 

 The Tindharia drift, however, was quite dry in the interior, although a 

 rivulet of water was trickling down the hill side directly above it. 

 The surface clay no doubt protects the out-crop, and it would probably 

 do so in many other cases also. In a thoroughly wet mine, it is to be 

 feared that the water would render the already soft coal so yielding 

 that the difficulty of keeping up the roof would be considerably 

 increased. 



The softness of the coal, although so disadvantageous in other re- 

 spects, has at least this in its favor, that the work of ' getting' the coal 

 would be easier. Instead of the laborious { holing under ', and subse- 

 quent breaking down by wedges or blasting, that is employed in most 

 mines, nothing is requisite but to dig the coal out with kodalis and 

 picks, as was done in the Tindharia drift. 



h ( 57 ) 



