Whenever the water came down into the fire, the hot rocks would be furious with indignation, and tearing the water to atoms they would throw it back to the surface as steam.  Then the explosive force of the steam would in turn tear up the rocks, making still larger the hole through which the water came.  When the rocks were very hot, a little water upon them would make a terrible commotion like the shock of an earthquake.  When much water came down, it would hiss and boil high in the air, as it tried to break the cushion of steam which came between it and the lava.

[Illustration:  MOUTH OF GEYSER.]

And all this went on 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 the snow cannot put out a mile deep of fire.