THE SEDIMENTARY NATIONAL PARKS
XII
ON SEDIMENTARY ROCK IN SCENERY
The national parks which are wrought in sedimentary rocks are Glacier, Mesa Verde, Hot Springs, Platt, Wind Cave, Sully's Hill, and Grand Canyon. Zion National Monument is carved from sedimentary rock; also several distinguished reservations in our southwest which conserve natural bridges and petrified forests.
Sedimentary rocks have highly attractive scenic quality. Lying in strata usually horizontal but often inclined by earth movements, sometimes even standing on end, they form marked and pleasing contrasts with the heavy massing of the igneous rocks and the graceful undulations and occasional sharp-pointed summits of the lavas.
As distinguished from igneous rocks, which form under pressure in the earth's hot interior, and from lava, which results from volcanic eruption when fluid igneous rocks are 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.