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BALL AND SIMPSON: COALFIELDS OF INDIA. 
the more economical " longwall " method, yet, owing to the 
thickness of the majority of Indian coal seams, it is not easy 
to devise any more suitable plan of working. It is undoubtedly 
wasteful, for the pillars form from 25 to G5 per cent, of the 
available coal, and at the present time their extraction is under- 
taken at only a limited number of mines. In the early days, and 
even now, at certain collieries, extremely small pillars were left to 
support the excavations ; with the result that after some time 
serious subsidences occurred, and not infrequently lives were lost. 
Under the present more enlightened management, however, these 
occurrences are likely to become fewer. In the Giridih field an 
extraction of more than 90 per cent, is obtained from a seam, 
21 feet thick, with an exceptionally strong roof. The pillars are 
formed in the lower part of the seam, and by an ingenious arrange- 
ment of vertical cuts, aided by the use of high explosives, succes- 
sive areas of the top coal 40 feet square are dropped, and filled 
away before the roof shows signs of breaking. The system has 
since been introduced with success in the Jharia coalfield. 
In the Raniganj field a thin seam was worked for some years on 
the longwall method with the use of disc coal cutters and a 
mechanical conveyor. With the decline in prices which followed the 
coal boom of 1907-08 the cost was found to be prohibitive and the 
experiment was given up in 1910. 
During the same period of inflated prices and scarcity of labour 
mechanical coal cutters of the pick type were introduced in a 
number of Bengal mines. Their use has since declined, but they 
are still employed in development work at a few collieries. 
At the Singareni collieries longwall working is practised to a 
small extent, and a few years ago the extraction of small pillars 
by a system of hydi'aulic or water-introduced packing was tried 
but abandoned on the score of excessive cost. 
In the Jharia coalfield a highly inclined coal seam 100 feet in 
thickness is being worked by a system of horizontal slices with fair 
success. In the same coalfield thick seams lying at a moderate 
inclination are being worked in stages with unworked layers of solid 
coal between. 
In the Makum coalfield (Assam), a highly-inclined seam, 75 feet 
thick, is worked on a modification of the South Staffordshire system 
of " square work." The coal is removed in two or sometimes 
three sections, the top section being removed first, and a parting 
