n value and, in the miner's view, only those
portions above the pay limit are ore-bodies, or ore-shoots. The
localization of values into such pay areas in an ore-deposit are
apparently influenced by:

1. The distribution of the open spaces created by structural
movement, fissuring, or folding as at Bendigo.
2. The intersection of other fractures which, by mingling of
solutions from different sources, provided precipitating
conditions, as shown by enrichments at cross-veins.
3. The influence of the enclosing rocks by:--
(a) Their solubility, and therefore susceptibility to replacement.
(b) Their influence as a precipitating agent on solutions.
(c) Their influence as a source of metal itself.
(d) Their texture, in its influence on the character of
the fracture. In homogeneous rocks the tendency
is to open clean-cut fissures; in friable
rocks, zones of brecciation; in slates or schistose
rocks, linked lenticular open spaces;--these
influences exhibiting themselves in miner's terms
respectively in "well-defined fissure veins,"
"lodes," and "lenses."
(e) The physical character of the rock mass and the
dynamic forces brought to bear upon it. This
is a difficult study into the physics of stress in
cases of fracturing, but its local application has
not been without results of an important order.
4. Secondary alteration near the surface, more fully discussed
later.

It is evident enough that the whole structure of the deposit is
a necessary study, and even a digest of the subject is not to be
compressed into a few paragraphs.

From the point of view of continuity of values, ore-deposits may
be roughly divided into three classes. They are:--

1. Deposits of the infiltration type in porous beds, such as
Lake Superior copper conglomerates and African gold bankets.
2. Deposits of the fissure vein type, such as California quartz veins.
3. Replacement or impregnation deposits on the lines of fissuring
or otherwise.

In a general way, the uniformity of conditions of deposition in
the first class has resulted in the most satisfactory continuity of
ore and of its metal contents. In the second, depending much upon
the profundity of the earth movements involved, there is laterally
and vertically a reasonable basis for expectation of continuity
but through much less distance than in the first class.

The third class of