urally raises the question as to whence it came. If it is a
recent placer, it may be comparatively easy to follow up the stream
channels to the head-water territory which is delivering the main mass
of sediment, and there to locate a vein in place. The problem is
complicated by multiplicity of tributaries and by large size of the
drainage areas. In such cases careful panning and testing of the gravels
at frequent intervals may show which of several tributaries are
contributing most of the values, and thus may further localize the area
of search. Many important mining districts, including Butte, Bisbee, the
Mother Lode region of southern California, the diamond fields of Africa,
and others, have been found by tracing up placers in this manner. In the
case of an older placer deposit, where the topography and drainage have
been much altered since its formation, or where the deposit has been
covered by later sediments, the problem is of course much more
difficult.

Much less than a commercially valuable placer deposit in unconsolidated
surface rocks may start a search for the mother lode. A single fragment
of ore in the "wash" naturally directs attention up the slope, and the
repetition of fragments in a certain direction may lead unerringly to
the source. The fragments may not even in themselves carry value, but
may consist of detrital material from the leached outcrop--such as iron
or manganese oxides, which, because of their red or black color, stand
out conspicuously in the rock debris.

In the Lake Superior region large angular fragments of iron ore or iron
formation in the glacial drift immediately raise question as to source.
If the fragments are rounded and small, they usually indicate a very
distant source. The general direction of glacial movement is known in
most places, and by tracing up the fragments in this direction the
outcrop may be found; or the chain of fragments may be traced to a point
where they stop, which point may serve to locate the parent bedrock
carrying the ore body, even though it does not outcrop.

An interesting suggestion was made some years ago with reference to the
diamonds found sporadically in the terminal moraines in Wisconsin and
other mid-west states. The diamonds are of such size and quality as to
indicate surely the existence of a real diamond field somewhere to the
north. The locations of these diamond finds were platted on a glacial
map, and lines were projected in a general nor