164 



RANIGANJ COAL FIELD. [Pt. II. ClIAP. II. 



pillars before abandoning the mine, and, on the other, for the quan- 

 tity of small coal and shale extracted, it is evident that, under the 



Fig. 10. Diagram showing mode of working at Raniganj Colliery. 



FT". 



I '■' 



Method of working coal in the Raniganj field, the shaded parts represent the coal, 

 the unshaded the galleries from which it has been extracted ; A A are the posts left 

 to support the roof. 



most favorable circumstances, not more than two-thirds of the coal 

 can ever be obtained in a marketable state, and in most collieries the 

 proportion is unquestionably much lower — probably not more than half. 

 In Raniganj mine the seam, as before described, has a thickness of 

 13 feet 2 inches, the section being — 



Ft. in. 



9 











3 







9 



... 



2 



3 







Hard black shale. 



Coal 



Shale parting 



Coal 



Shale parting 



Coal 



Under-bed of shale. 



Of this, the upper 9 feet bed is first removed by the method described, 

 and afterwards, the two thinner beds are extracted from the floor of 

 the galleries. The roof, which consists of shale, is slightly liable 

 to fall off in flakes when first opened, but this liability does not long 

 continue, and, even in galleries many years old, no "creep," or bulging 

 of either sides of floor and roof from pressure is perceptible. No 



