fotne Strata In Ireland and Scotland. 87 
May not the coal found at Ardlun be an indurated bitu- 
men, which, exuding in a liquid ftate from the incumbent 
matter, penetrated the argillaceous fhiftus, which previ- 
oufly conftituted the intervening ftratum between the lava ? 
It has fome of the properties of jet ; the fpecific gravity of 
that which we procured is 1,284; it is of a glofly black, its 
fradure glafly and conchoidal, does not foil the .fingers when 
handled, and when warmed by fridion will attract light bo- 
dies. Placed on a red-hot iron it decrepitates, emits a denfe 
fmoke which has a refinous fmell, becomes thoroughly ignited, 
burfts into flame, and yields an impalpable refiduum, which is 
not attraded by the magnet, and of which I only procured 
half a grain, of a yellowifh brown colour, from twenty grains 
of the crude fubftance. 
The learned Bifhop of Landaff, in the third volume of 
his Chemical EflTays, in his Effay on Bitumens (p. 6.), fup- 
pofes that, under certain circumftances, naphtha, petroleum, 
and afphaltum, might be produced by a kind of fubterraneous 
diftillation, and might impregnate the porous ftrata of feveral 
kinds of ftones and earth. Confider then, whether the fub- 
ftance I have been defcribing may not have been produced in 
that manner, Alice it is included within a mafs of matter 
which carries every appearance of having formerly been aded 
upon by fire. 
I am, &c. 
A. MILLS. 
P.S. If you compare the bearings which I have taken with 
the map in Mr. Pennant’s Voyage in 1772, they will be 
found to agree ; and if the variation of the needle be allowed, 
they will coincide with the map in Dr. Anderson’s Prefent 
State of the Hebrides. 
5 
LET- 
