e easily read
upon the bare deserts of our southwest than on the grass-concealed
prairies of the Mississippi Valley or the eroded and forested ranges of
the Appalachians.

Before the Rockies and the Sierra even existed, in the shallow sea which
covered this part of the continent were deposited the ooze which later,
when this region rose above the sea, became the magnificent limestones
of the Grand Canyon. Muds accumulated which to-day are seen in many
highly colored shales. Long ages of erosion from outlying mountain
regions spread it thick with gravels and sands which now appear in rocky
walls of deep canyons. A vast plain was built up and graded by these
deposits. The trunks of trees washed down by the floods from far distant
uplands were buried in these muds and sands, where, in the course of
unnumbered centuries, they turned to stone. They are the petrified
forests of to-day.

Mountains, predecessors of our modern Sierra, lifted in the south and
west, squeezed the moisture from the Pacific winds, and turned the
region into desert. This was in the Jurassic Period. Sands thousands of
feet deep were accumulated by the desert winds which are to-day the
sandstones of the giant walls of Zion Canyon.

But this was not the last desert, for again the region sank below the
sea. Again for half a million years or more ooze settled upon the sands
to turn to limestone millions of years later. In this Jurassic sea
sported enormous marine monsters whose bones settled to the bottom to be
unearthed in our times, and great flying reptiles crossed its water.

Again the region approached sea-level and accumulated, above its new
limestones, other beds of sands. New river systems formed and brought
other accumulations from distant highlands. It was then a low swampy
plain of enormous size, whose northern limits reached Montana, and which
touched what now is Kansas on its east. Upon the borders of its swamps,
in Cretaceous times, lived gigantic reptiles, the Dinosaurs and their
ungainly companions whose bones are found to-day in several places.

For the last time the region sank and a shallow sea swept from the Gulf
of Mexico to the Arctic Ocean. Again new limestones formed, and as the
surface very slowly rose for the last time at the close of the
Cretaceous Period many new deposits were added to the scenic exhibit of
to-day.

Meantime other startling changes were making which extended over a lapse
of time which human mind cannot gr