76 Notice on the Ball Coal of the Burdwan Mines. [Jan. 



We have thus at length an abundance of this remarkable variety of 

 coal, and it is impossible to examine it in the mass, and in detail, 

 without at once being satisfied that, as I conjectured in my second 

 notice, this is neither more nor less than coal softened by heat, and 

 taking when cooling this concretionary and semi-concretionary form 

 and in some instances, perhaps, indeed in the whole mass when seen in 

 situ it has adopted the semi-columnar appearance with a true ball and 

 socket joint, like basalt. One of Mr. Homfray's specimens indeed, is 

 a most splendid and perfect instance of this, being a fragment of what 

 we might term a carbonaceous shaft 7 or 8 inches in diameter, with a 

 complete ball and socket articulation ! Mr. Theobald in his note says 

 that " the seam in which the ball coal is found at Kumarcolly includ- 

 ing some partings, is 40 feet and upwards in thickness," he farther 

 adds " I should attribute the globular structure to a partial change 

 which in many places is effected by trap dykes." 



The larger balls are dull exteriorly, and marked with the alternate 

 bands of bright and dull coal of the mineral in its massive state, but 

 the glance (of the surface) brightens as the balls decrease in size, till 

 the very small ones of the size of an egg or a walnut become perfectly 

 bright and highly polished ; and in these all external trace of the 

 lamination* of the coal has disappeared. I have found in none how- 

 ever any of the pavoine lustre so common in the Anthracites. 



In the fracture of the small balls, traces of the lamination are at 

 times to be found; but generally these balls may be described as 

 composed of minute, irregularly set laminae, very bright and specular 

 like bright coal or coke-dust cemented or half melted together. 



The balls are rather tougher than the matrix coal. 



Whether in mass or in powder it swells considerably in the crucible, 

 and the coke is excessively slow and difficult of incineration and it has 

 the peculiarity of forming over the lamp, and in an open crucible 

 a kind of coke which must be pulverised to reduce it to ash in any 

 moderate time. It perfectly resembles in this respect the Anthracite 

 which seems to have its carbon in a state approaching to that in which 

 it exists in Plumbago. 



* By the lamination I mean the alternate bands of dull and bright Coal which all 

 our Indian Coals have, and which is found also in many European kinds of Coal. 



