om granite.
Sandstone is made of particles of quartz. Clay and slate are made out of
feldspar and mica. Iron ore comes from the hornblende in granite. The
mineral particles, reassembled in different proportions, form all of the
different rocks that are known.

Here in my hand is a piece of pudding-stone. It is made of pebbles of
different sizes, each made of different coloured minerals. The pebbles
are cemented together with a paste that has hardened into stone. This
kind of rock the geologists call _conglomerate_. Pudding-stone is the
common name, for the pebbles in the pasty matrix certainly do suggest
the currants and the raisins that are sprinkled through a Christmas
pudding.

Under the seashores there are forming to-day thick beds of sand. The
rivers bring the rock material down from the hills, and it is sorted and
laid down. The moving water drops the heaviest particles near shore, and
carries the finer ones farther out before letting them fall.

[Illustration: The town of Cripple Creek, Colorado, which has grown up
like magic since 1891, covers the richest gold and silver mines in the
world]

[Illustration: The level valley is filled up with fine rock flour washed
from the sides of the neighboring mountains]

The hard water, that comes through limestone rocks, adds lime in
solution to the ocean water. All the shellfish of the sea, and the
creatures with bony skeletons, take in the bone-building, shell-making
lime with their food. Generations of these inhabitants of the sea have
died, and their shells and bones have accumulated and been transformed
into thick beds of limestone on the ocean floor. This is going on
to-day; but the limestone does not accumulate as rapidly as when the
ocean teemed with shell-bearing creatures of gigantic size. Of these we
shall speak in another chapter.

The fine dust that is blown into the ocean from the land, and that makes
river water muddy, accumulates on the sea bottom as banks of mud, which
by the burden of later deposits is converted into clay. Sandstone is but
the compressed sand-bank.

In the study of mountains, geologists have discovered that old seashores
were thrown up into the first great ridges that form the backbone of a
mountain system. The Rocky Mountains, and the Appalachian system on the
east, were made out of thick strata of rocks that had been formed by
accumulations of mud and sand--the washings of the land--on the opposite
shores of a great mid-continen