ECONOMIC GEOLOGY
by tension, as when a sheet of rock is stretched by folding,
or shrinks during cooling or drying. The second kind of
fissures are formed along faults, i.e. where the rock on one
side of a fracture has been moved along it. Faults are
usually marked by slickensides or scratches on the walls,
and by a rubble of rock fragments known as fault-breccia.
Pug or fluccan (Cornish) or gouge (American) is material
that has been ground by the movement into clay. Faults
are usually not quite straight, but curve around harder
layers or masses. Owing to the curves the fault fissure
usually consists of lenticular Spaces, separated by the pro-
jections of the opposite walls coming into contact. The lode
or vein along such a fault alternately expands and contracts
and may consist of isolated lenticles of
ore. A lode in which the sides are not
parallel is known as a block-lode or wavy-
lode (Fig. 2) ; where the lode widens it
is said *‘ to make ; " where it contracts
it is said to ““ pinch * or “ peter.” The
‘hin streak along part of a fault plane
»n which there may be no lode matter,
sxcept perhaps a film of pug, is said to
be the “lode track,” as the miner ex-
pects it to lead him to the next * make”
of ore. If a fault crosses a series of
bedded rocks the fractures may be
diverted here and there along a bedding
plane, and the lode may therefore be repeatedly deflected
and may consist of steps; such step-lodes may be due to a
series of faults. Either the part along or across the bedding
plane may be represented by a lode track, and the actual
lode be reduced to a series of parallel isolated sections.
A vein parallel to the bedding of the rocks is a bedded-
vein, a vein transverse to the country, if confined to one
bed, is a gash-vein, but if it cut across several beds, it is
a rake-vein.
Lodes are usually steeply inclined ; if horizontal they are
often known as “floors.” If formed along more or less
horizontal faults they are sometimes known as “slides.”
Floors often occur one below another in a dyke or narrow
intrusion of igneous rock ; these floors are formed along
