COAL AFFECTED BY BASALTIC ERUPTION. 127 



height of fifty to sixty feet above the lower ground where the mouth of the shaft was 

 placed. 



s.w. 



Broken Basalt. 

 Beds of Coal. 



Various old pits had been sunk at short distances from the wall of basalt, but the 

 speculators had always avoided trials at this very spot, for it was supposed to be pre- 

 cisely upon the continuation of the " Jewstone fault." After penetrating about twenty 

 feet of rotten Jewstones, various measures were passed through, and three of the four 

 beds of coal so well known in these hills were proved. On following the coals (a, a, a,) 

 to the north-east or towards the edge of the plateau of basalt, the three-quarter and the 

 great coal were both found to change their characters, and to become lighter and of 

 little value, and still nearer the basalt they were completely changed into a sort of dull 

 sooty substance, in which all the structure of coal was lost, but in which were dissemi- 

 nated many small flakes of anthracite. This altered mass (b, b,) was further disco- 

 vered to be in contact with a wall of basalt (c, c,) which, flanking the charred accumu- 

 lations, bulged over it irregularly as represented in the wood-cut. The ends of the coal 

 seams in contact with the basalt were slightly turned up, and the junction stuff" was 

 coloured red, most probably by the decomposition of the adjoining basalt which was 

 in the state of " rotten Jewstone 1 " for a width of four or five feet. The three upper 

 coals and ironstone measures were all in their regular places. The lower coal was not 

 proved, owing to the inferior condition of the overlying seams. The following remark- 

 able circumstances attend this junction of coal and basalt. 



1st. The altered condition of the great coal; the light black matter proving on 

 examination to be still bituminous and to give off flame under the blowpipe, so that 

 however the change in its composition may have been effected it is still capable of 

 yielding carburetted hydrogen gas. The separation from this sooty mass of the small 

 crystalline flakes of anthracite is also a curious fact and worthy of attention. 



2ndly. The Smith coal was zmaltered notwithstanding the marked changes observed in 

 the overlying coals, an anomaly which is left for the chemist to explain. 



The width of the basaltic dyke being ascertained to be about one hundred and fifty 



1 The miner's term for decomposing basalt. 



q2 



