On the Tenasserim Coal Field. 421 



and fragments of slate, denote the primitive structures of the moun- 

 tains on that side of the river. The only other rock in the neigh- 

 bourhood is a ferruginous gritstone, dipping immediately below the 

 coal beds ; but I saw in it no character to allow of its being placed 

 so low as the carboniferous system. 



The shales from the roof of the coal have numerous vegetable im- 

 pressions, but of small size, and they appear to be allied to existing 

 species. The series of beds above the coal which are seen in the 

 opposite side of the river, and will be hereafter described, amounting 

 to 500 feet, consist chiefly of soft shales of various colours, sand- 

 stone, and shale conglomerate, composed of the debris of other strata 

 similar to their own. They are also intersected in two places by 

 parallel dykes of igneous rock, but none of them seem to have under- 

 gone that degree of pressure and solidification, which is apparent in 

 coal measure shales of the older periods, nor have there been yet 

 seen any remains of organic substances amongst them to authorize 

 their being referred thereto. 



10. In the absence of guides by which these questions are usu- 

 ally decided, and with the anomalous character of the adjoining rocks, 

 the true nature of the coal must be determined by external charac- 

 ters, by its behaviour in the fire, and by its composition. 



11. It is found in a hard and solid bed, consisting of layers of slaty 



structure parallel to the bed, and is easily separated in that direction. 



Between the laminae there are thin plates of arsenical iron pyrites. 



It is bright to the surface in cuboidal pieces, which do not however 



preserve their size under rough treatment. Its cross fracture is 



conchoidal, and it is fibrous, dividing into thin plates in the opposite 



direction, while its flat surfaces present a ringed appearance, much 



resembling the ringing of wood, as seen in transverse sections. Its 



lustre is somewhat glistening when freshly broken in the mine, and 



colour dull black, but after exposure to the atmosphere it loses this 



appearance, and assumes a brownish black colour. It does not soil 



the fingers, but is deficient in that " glow," or metallic lustre, which is 



eminently characteristic of mineral coal. Its specific gravity is 1.2. 



In the flame of a spirit lamp it exhibits some inflammable gas, and 



gives off a small quantity of brown oily bitumen ; it does not swell, 



and emits but little smoke. It consists chiefly of carbon, and leaves 



when well burnt, a very small proportion of residue. 



3 i 



