DAMUDA SERIES. 15 



quartzites, the shales into splintery slates, and the carbonaceous shales 

 into carbonaceous or even graphitic schists ; while the coal has lost a 

 large proportion of its volatile matter, so as to approach to anthracite in 

 composition. Thus while the assays of samples from seventeen seams in 

 the Raniganj field * show an average composition of carbon 51*09, 

 volatile matter 32*64, ash 16*27, the mean result from five Darjiling 

 seams gives carbon 70*66, volatile matter 9*20, ash 20*14. At the same 

 time, the crushing to which the seams have been subjected, has squeezed 

 them so that they vary greatly in thickness within a few yards, and has 

 induced a flaky structure in the coal which renders it so friable that it 

 can be crumbled into powder between the fingers with the greatest ease. 

 This flakiness is in fact true cleavage, and the mineral may in one sense * 

 be regarded as a ' coal slate/ 



The coal seams being the least strongly coherent of the Damuda 

 rocks, faults would be most likely to occur along them when nearly 

 vertical. Hence, perhaps, in some cases the rapid variations in the thick- 

 nesses of the seams, and the crushed state of the coal, it having been 

 ground between the two sides of the fault. I cannot bring forward any 

 instances in which faulting can be shown to have acted in this way ; it is 

 probable, however, that they exist, although in the great majority of 

 cases, simple crushing without actual dislocation has reduced the seams 

 to their present condition. 



The amount of metamorphism in the Damudas is by no means con- 

 stant : generally the beds are more or less altered, and not unfrequently 

 highly so, but sometimes there is no alteration whatever, and the rocks 

 closely resemble the typical ones of the Raniganj field. The coal is an 

 exception, as it everywhere has acquired the above flaky structure, even 

 when the beds accompanying it have undergone no appreciable change. 



The vegetable mould and clay beneath the dense jungle by which 

 the hills are covered, render good outcrops rare, except in the beds of the 



* Vol. Ill, p. 189. 



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