the Smithsonian Institution in the French provinces of North
Africa. In earlier times, throughout the length of the cordillera
great masses of volcanic material were poured out to form high
plateaus like those of southern Mexico or of the Columbia River
in Oregon. In Utah some of these have been lifted up so that
heavy caps of lava now form isolated sheets topping lofty
plateaus. There the lowland shepherds drive their sheep in summer
and live in absolute isolation for months at a time. There, as
everywhere, the cordillera bears the marks of mountains in the
making, while the mountains of eastern America bear the marks of
those that were made when the world was young.

The geysers and hot springs of the Yellowstone are another proof
of recent volcanic activity. They owe their existence to hot
rocks which lie only a little way below the surface and which not
long ago were molten lava. The terraces and platforms built by
the geysers are another evidence that the cordillera is a region
where the surface of the earth is still being shaped into new
forms by forces acting from within. The physical features of the
country are still in process of construction.

In spite of the importance of the constructive forces which are
still building up the mountains, much of the finest scenery of
the cordillera is due to the destructive forces of erosion. The
majestic Columbia Canyon, like others of its kind, is the work of
running water. Glaciers also have done their part. During the
glacial period the forces which control the paths of storms did
not give to the cordillera region such an abundance of snow as
was sifted down upon Laurentia. Therefore no such huge
continental glaciers have flowed out over millions of square