of 82 per cent shale, 12 per cent sandstone, and 6 per cent limestone.
Only this combination of the three sediments will yield an average
composition comparable with that of the parent igneous rocks. As
actually observed in the field the sandstones and limestones are in
relatively higher percentage than is here indicated, suggesting that
part of the shales may have been deposited in deep seas where they
cannot be observed, and that part may have been so changed or
metamorphosed that they are no longer recognized as shales.

SOILS AND CLAYS

Weathered and disintegrated rocks at the surface form soils and clays.
No estimate is made of abundance, but obviously the total volume of
these products is small as compared with the major classes of earth
materials above noted, and in large part they may be included with these
major classes.

WATER (HYDROSPHERE)

It has been estimated that all the water of the earth, including the
ocean, surface waters, and underground waters, constitutes about 7 per
cent of the volume of the earth to a depth of 10 miles.[3]

COMPARISON OF LISTS OF MOST ABUNDANT ROCKS AND MINERALS WITH COMMERCIAL
ROCKS AND MINERALS

Of the common rocks and minerals figuring as the more abundant materials
of the earth's crust, only a few are prominently represented in the
tables of mineral resources. Of these water and soils stand first.
Others are the common igneous and sedimentary rocks used for building
and road materials. Missing from the lists of the most abundant minerals
and rocks, are the greater part of the commercially important mineral
resources--including such as coal, oil, gas, iron ore, copper, gold, and
silver,--implying that these mineral products, notwithstanding their
great absolute bulk and commercial importance, occur in relatively
insignificant amounts as compared with the common rock minerals of the
earth.

THE ORIGIN OF COMMON ROCKS AND MINERALS

The common rocks and minerals develop in a general sequence, starting
with igneous processes, and passing through stages of weathering,
erosion, sedimentary processes, and alterations beneath the surface. The
commercial minerals are incidental developments under the same
processes.

IGNEOUS PROCESSES

The earliest known rocks are largely igneous. Sedimentary rocks are
formed from the breaking down of igneous rocks, and the origin of rocks
therefore starts with the formation of igneous rocks. Igneous rocks are
formed by the co