MINERALS. 33 q 
abundant, and so noxious, that, in order to avoid 
suffocation, the miners are obliged to fly to the 
pits or galleries, otherwise they would be instantly 
destroyed by the arsenical and sulphureous par- 
ticles. Sulphur and arsenic are commonly found 
m the four imperfect, and in all the semimetals, 
and it is from these they receive their metallic 
form.” 
It is not the noxious vapours alone that the 
miners have to contend with, as they equally run 
the hazard of having a portion of the mine fall 
upon them and burying them in the ruins. This 
accident of course is more likely to occur in some 
situations than m others, and especially in mines 
where the looking-glass lead ore, or, as the miners 
call it, slickensides, abounds. ^ he curious account 
of this mineral which Mr. Whitehurst, in his Ob- 
seivations on the Strata of Derbyshire, has given us, 
wall point out the necessity of mining with caution 
in its neighbourhood. 
“ To what has been said of earthquakes,” says 
Mr. Whitehurst, “ I shall here add an account of a 
subterraneous explosion, which happens from a very 
obscure cause, in a sort of fossil called the slicken- 
sides. This stone has the appearance of black 
marble, and breaks when the explosion happens, 
with a polished surface not truly plane, hut lying- 
in waves. It is found in fissures of lime-stone in 
HayclifF and Lady wash mines at Eyam, and in 
Oden, at Castleton in Derbyshire. It is divided 
into two equal parts or slabs, by a line parallel to 
z 2 
