They are common even in cases where there has been no shift, and
occur equally in non-metalliferous fissures. They are called by miners "slicken-
sides," from the German schlichten, to plane, and seite, side. It is supposed
that the lines of the striae indicate the direction in which the rocks were
moved.
In some of the veins in the mountain limestone of Derbyshire, containing lead,
the vein-stuff, which is nearly compact, is occasionally traversed by what may
be called a vertical crack passing down the middle of the vein. The two faces in
contact are slicken-sides, well polished and fluted, and sometimes covered by a
thin coating of lead-ore. When one side of the vein-stuff is removed, the other
side cracks, especially if small holes be made in it, and fragments fly off with
loud explosions, and continue to do so for some days. The miner, availing
himself of this circumstance, makes with his pick small holes about six inches
apart, and four inches deep, and on his return in a few hours finds every part
ready broken to his hand. (Conybeare and Phil. Geol. page 401 and Farey's
Derbyshire page 243.
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