Mr. Forster's Notice of a Basaltic Dyhe. 49 



first introduction into a strong heat, the powdered Coke emitted a feeble 

 blue flame for a few seconds, but it may be observed that so great is the 

 proportion of earthy matter, both in this Coke and the specimen from 

 the Lower Seam, that they are equally unfit for the purposes of ordinary 

 combustion. 



Nos. 6 and 7> are specimens of Basalt from the 10-feet stratum in the 

 William pit. Specific gravity of No. 6, 27OI ; and of No. 7, 2-758. 



Bemarks. The proportion of incombustible earthy residuum existing 

 in the carbonized Coal, from both seams, may, I think (in conjunction 

 with the great pressure under which the process of coking would, in this 

 instance, take place}, be considered as very fairly accounting for the 

 great specific gravity of the Coke as compared with the Coal. That 

 pressure has very materially assisted in producing this effect, may be in- 

 ferred from the great compactness and weight of the Coke, from the 

 Lower or Main Coal Seam ; which, owing to its depth, would sustain a 

 greater degree of compression than the Upper Seam, and hence, although 

 its proportioh of earthy matter is less, its specific gravity is greater than 

 than that of the 10-feet stratum of Coke, representing the Upper Seam. 

 With regard to the earthy residuum itself, its presence in so large a 

 quantity appears difficult to account for ; unless, indeed, it may be sup- 

 posed to be Basaltic matter, which has been infused into the cavities left 

 by the escape of the volatile products of the Coal, when heated by its 

 contiguity to the Dyke, and its contact with the Basalt, with which it is 

 interstratified. 



Ne'wcastle upon Tyne, March 16, 1830. 



VOL. I. 



