re released from pressure,
sedimentary rocks are formed by the solidification of precipitations in
water, like limestone; or from material resulting from rock
disintegrations washed down by streams, like sandstone and shale. The
beds in which they lie one above another exhibit a wide range of tint
and texture, often forming spectacles of surpassing beauty and
grandeur.

These strata tend to cleave vertically, sometimes producing an
appearance suggestive of masonry, frequently forming impressive cliffs;
but often they lie in unbroken beds of great area. When a number of
well-defined strata cleave vertically, and one end of the series sags
below the other, or lifts above it, the process which geologists call
faulting, the scenic effect is varied and striking; sometimes, as in
Glacier National Park, it is puzzling and amazing.

Many granitic and volcanic landscapes are variegated in places by
accidental beds of sedimentary rock; and conversely occasional
sedimentary landscapes are set off by intrusions of igneous rocks.

Besides variety of form, sedimentary rocks furnish a wide range of color
derived from mineral dyes dissolved out of rocks by erosion. The
gorgeous tint of the Vermilion Cliff in Utah and Arizona, the reds and
greens of the Grand Canyon and Glacier National Park, the glowing cliffs
of the Canyon de Chelly, and the variegated hues of the Painted Desert
are examples which have become celebrated.

Geologists distinguish many kinds of sedimentary rocks. Scenically, we
need consider only four: limestone, conglomerate, sandstone, and shale.

Limestone is calcium carbonate derived principally from sea-water,
sometimes from fresh water, either by the action of microscopic
organisms which absorb it for their shells, or occasionally by direct
precipitation from saturated solutions. The sediment from organisms,
which is the principal source of American scenic limestones, collects as
ooze in shallow lakes or seas, and slowly hardens when lifted above the
water-level. Limestone is a common and prominent scenic rock; generally
it is gray or blue and weathers pale yellow. Moisture seeping in from
above often reduces soluble minerals which drain away, leaving caves
which sometimes have enormous size.

The other sedimentary rocks which figure prominently in landscape are
products of land erosion which rivers sweep into seas or lakes, where
they are promptly deposited. The coarse gravels which naturally fall
first bec