nto mountain form. Now, cold and hard, these masses are
disclosed as the granite of to-day's landscape, or as other igneous
rocks of earth's interior which now cover broad surface areas, mingled
with the stratified or water-made rocks which the surface only produces.
But this has not always been the fate of the under-surface molten rocks,
for sometimes they have burst by volcanic vents clear through the crust
of earth, where, turned instantly to pumice and lava by release from
pressure, they build great surface cones, cover broad plains and fill
basins and valleys.

Thus were created the three great divisions of the rocks which form the
three great divisions of scenery, the sediments, the granites, and the
lavas.

During these changes in the levels of enormous surface areas, the frosts
and water have been industriously working down the elevations of the
land. Nature forever seeks a level. The snows of winter, melting at
midday, sink into the rocks' minutest cracks. Expanded by the frosts,
the imprisoned water pries open and chips the surface. The rains of
spring and summer wash the chippings and other debris into rivulets,
which carry them into mountain torrents, which rush them into rivers,
which sweep them into oceans, which deposit them for the upbuilding of
the bottoms. Always the level! Thousands of square miles of California
were built up from ocean's bottom with sediments chiselled from the
mountains of Wyoming, Colorado, and Utah, and swept seaward through the
Grand Canyon.

These mills grind without rest or pause. The atmosphere gathers the
moisture from the sea, the winds roll it in clouds to the land, the
mountains catch and chill the clouds, and the resulting rains hurry back
to the sea in rivers bearing heavy freights of soil. Spring, summer,
autumn, winter, day and night, the mills of Nature labor unceasingly to
produce her level. If ever this earth is really finished to Nature's
liking, it will be as round and polished as a billiard ball.

[Illustration: _From a photograph by Bailey Willis_

MIDDLE FORK OF THE BELLY RIVER, GLACIER NATIONAL PARK

Very ancient shales and limestone fantastically carved by glaciers. The
illustration shows Glenns Lake, Pyramid Peak, Chaney Glacier, and Mount
Kipp]

Years mean nothing in the computation of the prehistoric past. Who can
conceive a thousand centuries, to say nothing of a million years? Yet
either is inconsiderable against the total lapse of time even from