ons take into account all of the geologic
and economic factors ascertainable. The classes of mineral land
designated vary with the mineral, the district, and the purpose for
which the classification is made.

Common procedure for commercial exploration purposes is to divide the
lands of a given territory into three groups--(1) lands which are
definitely promising for mineral exploration, (2) lands of doubtful
possibilities, and (3) lands in which the mineral possibilities are so
slight that they may be excluded from practical consideration. Each of
these classes may be subdivided for special purposes. Another commonly
used classification is, (1) proved mineral lands, (2) probable mineral
lands, usually adjacent to producing mines, (3) possible mineral lands,
and (4) commercially unpromising mineral lands.

The classification of the public mineral lands by government agencies is
fully discussed by George Otis Smith and others in a bulletin of the
United States Geological Survey.[37] The purposes, methods, and results
of this classification should be familiar to every explorer. Nowhere
else is there available such a vast body of information of practical
value. Quoting from this report:

A study of the land laws shows the absolute necessity of some
form of segregation of the lands into classes as a
prerequisite to their disposition. Agricultural entry may not
be made on lands containing valuable minerals, nor coal entry
on lands containing gold, silver, or copper; lands included in
desert entries or selected under the Carey Act must be desert
lands; enlarged-homestead lands must not be susceptible of
successful irrigation; placer claims must not be taken for
their timber value or their control of watercourses; and lands
included in building-stone, petroleum, or salt placers must be
more valuable for those minerals than for any other purpose.
So through the whole scheme of American land laws runs the
necessity for determining the use for which each tract is best
fitted.

For this purpose the Geological Survey has made extensive classification
of coal lands, oil and gas lands, phosphate lands, lands bearing potash
and related salines, metalliferous mineral lands, miscellaneous
non-metalliferous mineral lands, and water resources. The scope of the
work may be indicated by the factors considered. For instance coal is
investigated in relation to its char