l of particles of sand. You cannot get away from
it.

_Aluminum_ is a light, bluish-white metal which we know best in
expensive cooking utensils. It is more abundant even than iron, but
processes of extracting it from the clay are still expensive. It is
oftenest found in combination with oxygen and silicon. While nearly
one-tenth of the earth's crust is composed of the metal aluminum,
four-fifths and more is composed of the minerals called silicates of
aluminum--oxygen, silicon, and aluminum in various combinations. It is
more plentiful than any other substance in rocks and in the clays and
ordinary soils, which are the finely ground particles of rock material.

_Iron_ is one of the commonest of elements. We know it by its red
colour. A rusty nail is covered with oxide of iron, a combination which
is readily formed wherever iron is exposed to the action of water or
air. You have seen yellowish or red streaks in clefts of the rocks. This
shows where water has dissolved out the iron and formed the oxide. The
red colour of New Jersey soil is due to the iron it contains. Indeed,
the whole earth's crust is rich in iron which the water easily
dissolves. The roots of plants take up quantities of iron in solution
and this mounts to the blossoms, leaves, and fruit. The red or yellow
colour of autumn leaves, of apples, of strawberries, of tulips, and of
roses, is produced by iron. The rosy cheeks of children are due to iron
in the food they eat and in the water they drink. The doctor but follows
the suggestion of nature when he gives a pale and listless person a
tonic of iron to make his blood red.

Iron is rarely found free, but it forms about five per cent. of the
crust of the earth, and it is believed to form at least one-fifth of the
unknown centre of the earth, the bulk of the globe, the weight of which
we know, but concerning the substance of which we can say little that is
positive.

_Manganese_ is not a conspicuous element, but is found united with
oxygen in purplish or black streaks on the sides of rocks. It is
somewhat like iron, but much less common.

_Calcium_ is the element that is the foundation of limestones. The
skeletons and shells of animals are made of calcite, a common mineral
formed by the uniting of carbon, oxygen, and calcium. Marbles are,
perhaps, the most permanent form of the limestone rocks. "Hard" water
has filtered through rocks containing calcite, and absorbed particles of
this mineral. From wa