C 536 ] 
very fimilar to thofe, which are generally found on 
the top of coal mines. The clay all'o (at lead; that 
part of it, which lies neareft to the coal) feems to 
partake of its nature, having fomewhat of a laminous 
texture, and being in a fmall degree inflammable j and 
amongft this clay, but adhering to the veins of coal, 
are found lumps of a bright yellow loam, extremely 
light, and fo faturated with petroleum, that they 
burn like fealing wax, emitting a very agreeable and 
aromatic fcent. 
Though the fubftance and quality of this coal, in 
its feveral ftrata, are much alike, and it is all indif- 
criminately ufed for the fame purpofes j yet there is 
lome difference in the colour, form, and texture, of 
the feveral veins. The exterior parts, which lie 
neareff to the clay, have a greater mixture of earth, 
and are generally of a dark brown, or chocolate 
colour ; fome of them appear like a mafs of coal and 
earth mixed ; others have a laminous texture, but 
the laminae run in fuch oblique, waving, and undu- 
lating forms, that they bear a ftrong refemblance to 
the roots of trees, of which kind I have feen fome 
l'pecimens from Lough Neagh in Ireland, which feem 
to be the fame fort of foffil. 
There are other veins of this coal, which lie more 
in the center of the ftrata, and abound moll in the 
lowed; and thickeft bed, the fubftance of which is 
more compact and folid : thefe are as black, and al- 
moft as heavy, as pit coal ; they do not fo eaftly di- 
vide into laminae, and feem to be more ftrongly im- 
pregnated with bitumen': thele are diftinguidied by 
the name of done coals, and the fire of them is more 
ftrong and lading than that of other veins. 
But 
