256 Mr. AiKiN on a Bed of Trap 



of the coal formation. This however is by no means the case 

 with the three beds that he immediately below the greenstone, 

 namely, the indurated sandstone, the carbonaceous slaty clay, and 

 the blind coal. 



The indurated sandstone is of a yellowish grey colour, dense, com- 

 pact and ponderous ; it consists essentially of fine grains of quartzy 

 sand and silvery mica, and contains very slender imperfect veins of 

 calcareous spar, and small irregular granular concretions of ferrife- 

 rous carbonate of lime : these concretions decompose by exposure to 

 the air, and give the external surface of the stone a brownish 

 yellow ochry tinge. In the specimens that have come under my 

 notice, the surface of the greenstone where it is in contact with 

 the sandstone, is of a brown colour, and decomposed to the 

 depth of an inch or more j but I have not observed any direct 

 mutual penetration of the two beds. The lower part of the sand- 

 stone, however, is considerably broken, and angular pieces of the 

 carbonaceous slaty clay (technically called batt^ occur, completely 

 involved in the sandstone. 



The characters of the batt, if taken from that part of the bed 

 where it is not covered by the greenstone, are those of common 

 bituminous shale or soft slaty clay, inclosing seams of pitch coal 

 about one-f.fth of an inch in thickness : but wherever this bed is 

 covered by the greenstone, the slaty clay is considerably indurated, 

 the ccai is also harder and more compact, and possesses a brilliant 

 semi-metallic lustre; and both the clay and the coal are wholly 

 destitute of bitumen. 



Below the batt lies a coal four feet thick, which, where covered 

 by the greenstone, has a shining somewhat iridescent lustre ; it is 

 entirely destitute of bitumen, and when put in the fire burns 

 rapidly, like common cinder, difiering materially in this respect 



