ECONOMIC GEOLOGY, 79 



than that in which no regular structure is apparent. There is a grada- 

 tion from the hard to the soft coals, no hard line existing between them. 



The soft coals are very tender at the outcrop. For some distance— 



a few inches or feet — from the surface, they are 

 Soft coal. I-. Ti 



weathered and sodden. The portion immediately 



below, which is often separated rather sharply from the sodden part, is 

 very tender, so that most of it crumbles into slack or small coal, and 

 what remains in lumps is too fragile to bear rough usage. But there is 

 reason to believe that this part also has been acted on by the weather, 

 and that many, at least, of such coals are compact enough at a few yards 

 from the surface when freshly exposed. The main causes to which the 

 brittleness of these coals is due seem to be, (1) lamination, giving the 

 coal a tendency to exfoliate ; (2) jointing on a small scale, which some- 

 times divides it into small pieces ; (3) the presence of minutely dissemin- 

 ated pyrites, the sulphates, resulting from the oxidation of which, in 

 crystallizing cause the coal to exfoliate and to split along the joints, and 

 sometimes (4) crushing of the coal from pressure. The unalterable 

 character of the hard coal appears to be mainly due to the absence of 

 these conditions. But it remains to be seen whether the same seam 

 retains its character throughout in this respect. Between two and three 

 hundred yards from the Dikhu there is an outcrop of the 4' Tel Pung 

 seam (p. 25), at which the coal must have been exposed for years without 

 deterioration. In the same seam a quarry was worked last cold weather 

 near the bank of the Dikhu 30 feet above the water. A sample of coal 

 about a cubic foot in size, which was hard and sound at the time, was 

 taken in December and carefully packed away. Five months later it 

 was found to have broken up into small pieces, which were studded with 

 minute crystals of copperas. The amount of pyrites in this coal was not 

 large, the total quantity of ash being only 3*2 per cent. 



Sometimes part of a seam, measured vertically, is hard and the rest 

 soft, like No. 3 in the Disang, but more commonly the seam has much 

 the same character throughout. 



( 347 ) 



