128 Correspondence. 



The effect produced upon the coal by the dykes is, in all the three 

 cases precisely the same : in their neighbourhood it is of a lighter co- 

 lour, duller, though in some parts it has a semi-metallic lustre, tougher, 

 porous, and its seams are bent, in every respect resembling coke, except 

 in its specific gravity and hardness, which are both greater. But as 

 these two circumstances may fairly be attributed to the weight of the 

 superincumbent strata, they do not oppose the hypothesis of the heated 

 state of the rock, supported by the other appearances. The specimens 

 marked A, corroborate the hypothesis of the fluid state of the dykes 

 at the time they pierced the coal, as they were taken in situ, above the 

 uppermost bed, and contain angular fragments of coal in a charred 

 state. Indeed in the one marked A. 2, the coal, or rather anthracite, is 

 columnar, a form produced by heat upon coal, as well as some other 

 substances, as is to be seen at all the Railroad coking furnaces, 

 where the whole mass of coke divides into columns, standing normally 

 to the surface of the furnace. 



The quantity of effect, or the distance to which the effect extends, is 

 not equal in the three cases, but, as was to be expected, proportionate to 

 the thickness of the dyke. In the case of No. 1, the coal is not altered 

 more than 11 or 12 inches from the surface of contact, while in the 

 other two, it is to a much greater distance. 



Generally the coal adheres so firmly to the dyke, as to break with it, 

 like one stone. 



Besides the specimens properly belonging to the above description, 

 I send you a piece of coal which I took from the bed alluded to in the 

 descriptions of Figs. 1 and 2, within a few feet of the dyke No. 1, to 

 serve for comparison with the charred part, to shew the degree of alter- 

 ation which the latter has suffered. 

 7, Banshtollah Gully, 



March \±th, 1841. 



