in hundreds of places and maybe for thousands of
years. The hot rocks glowed and sweltered in the ground, and the cold
snow-water crept after them closer and closer, while more and more
vigorously the rocks resented the intrusion. Sometimes the water would
go down in a mass through a cleft, when it would be hurled bodily the
very way it came. At other times the water came down little by little,
insinuating itself into many places at once. Then the hot rocks threw
it back in many little honeycomb channels, and by the spreading of
these channels the rocks were at last crumbled to pieces. The hard
black lava on the glass-like obsidian were changed to white kaolin as
soft and powdery as chalk. And as the water fought its way, gaining a
little every year, steadily working between the joints in the enemy's
armor and as surely being thrown back with violence if it penetrated
too far, the animals and the plants followed in the wake of the
water, and took possession of the territory as fast as it was won.

At last the Pliocene times were over, for all times come to an end.
The one sure thing on the earth is the certainty of change. With the
change of time came on the earth's great winter. The snow-drifts on
the lava were piled up mountain-high. Snow is but ice gathered in
little fragments which will grow solid under pressure. As the snow
accumulated it began to move, forming great rivers of ice which ran
down the courses of the stream. And as these slowly moving, gigantic
ice-rivers tore away huge blocks of lava and pushed them down the
mountain-sides, where the rocks had been softened by the action of
steam, the ice wore out deep valleys, and everything that it touched
was smoothed and polished. The winter of the great Ice age lasted a
very long time, many thousands of years; but, long as it was and long
ago, it came at last to an end--not to a full stop, of course, for
even now, some of its snow still lingers on the highest peaks that
surround the lava-beds.

[Illustration: "CUTTING DEEP GORGES OR CANONS."]

Then the winters grew shorter and the summers longer. The south winds
blew and the ice melted away, first from the plain and then from the
mountains. The water ran down the sides of the lava-bed, cutting deep
gorges or canons, so deep that the sun can hardly see the bottom. And
into the joints and clefts of the rocks more and more water went, to
be hurled back with greater and greater violence, for all the waters
of all