ECONOMIC GEOLOGYo 83 



lamiuatioiij that it is difficult to find any traces of bedding in hand 

 specimens. The color of the streak or powder is a lighter brown than 

 that of the Raniganj coal. 



A list of assays of 17 Raniganj coals may be found in Vol. III^ 

 page 189, which compares thus with the assays of Assam coals given 

 above : — 



Fixed carbon. Volatile matter. Ash. 



Average composition of 27 Assam coals ... 60'0 36*2 3'8 



Ditto of 17 Raniganj coals... Sl'l 32-6 16-3 



The Assam coals contain, on an average, more carbon than the Raniganj, 

 and only one-fourth the amount of ash. As samples of the best class 

 of coal from each field, we may take the following : — 



Fixed carbon. Volatile ma:tter. Ash. 

 4'seam, TelPung, DikhuvaHey (I) ... 66-0 32-0 2-0 



Sanktoria seam, Eaniganj ... ... 63'3 27*5 9*2 



The coal has hitherto been worked merely by surface scratchings 

 that can hardly be dignified by the name of 

 Quari^ing and mining, q^^rries, and necessarily the amount raised has 

 been quite insignificant. With few exceptions, the seams are most 

 unfavorably placed for open workings. Dipping, as they generally do, 

 at high angles in the opposite direction to the slope of the hill, it is 

 easy to see that, at a very small distance from the outcrop, the 

 ' overburden, ' or superincumbent soil and rock, must attain a thickness 

 too great to allow of the quarry being carried further. Thus, the slope 

 of the hill being 30° and the dip of the coal 30° also (a lower dip than 

 is very commonly met with), the depth of overburden will equal the dis- 

 tance from the outcrop measured parallel to the dip of the bed. In 

 quarrying such a seam, 10 feet thick, at no greater distance than 10 

 yards from the outcrop, the depth of overburden will amount to treble 

 the thickness of the coal. With higher dips the difficulty becomes still 

 greater. Hence the invariable fate of such quarries, in seams of moder- 

 ate thickness, is either collapse from undercutting the coal, or voluntary 



{ 351 ) 



