56 mallet: geology of darjiling and western duars. 



from that pursued in the Raniganj collieries, where the greatest dip of 

 the worked seams does not, as I am informed by Mr. Hughes, exceed ten 

 or twelve degrees. Coal mining in highly inclined strata is always 

 more difficult than in horizontal ones, but in many European fields, like 

 those of Belgium, Westphalia, and some of those in England, fuel is 

 profitably extracted from highly contorted seams. Where the folds of the 

 strata are on a sufficiently large scale, so that the dip is tolerably constant 

 for some distance, the coal can be worked at any inclination. But when, 

 in addition to such larger curves, the seams are further crumpled up by 

 other contortions on a minor scale, the difficulties are vastly increased, 

 and may become so great as to render the coal valueless. Now, in 

 the previous part of this report, I noticed several instances in which the 

 Darjiling seams are affected in this way, or where they are crushed into 

 small and violent contortions, and even doubled back sharply on them- 

 selves. This is decidedly the most unfavourable feature present. The 

 coal in many places will be unworkable in consequence, and it is even 

 possible that this condition may be so prevalent as to prevent any portion 

 being worked to a profit. The rapid variations in the thicknesses of 

 the seams, a consequence of the same crushing, is another element to be 

 taken into consideration, although of much less importance than the 

 contortions. The crushing has, further, more or less shattered the 

 sandstone and shale beds, or their equivalents where metamorphosed, 

 so that these rocks cannot be expected to furnish as firm a roof as the 

 same strata where undisturbed. The existence of faults and minor slips 

 is also to be expected, and if of frequent occurrence, these would add 

 another grave difficulty to working the coal. When describing the 

 Damiidas, I noted some instances of the occurrence of such slips. 



In the more highly inclined seams, the coal itself would form the 

 roof of the galleries, and as it is far too soft to be self-supporting, there 

 would be a heavy item of expense for timbering ; an item which does not 

 exist in the Raniganj mines worked on the post and stall system, where 



( 56 ) 



