"The black is the dark green of the growing pine timber, and the grey is where the timber has been burned, and is dead. For the first year or two after the fire has passed over the forest and killed them, the trees are black or keep their bark. Then the wind and rain and snow beating on the soft coating of charcoal, wear off the charred surface and the bark, and the wood becomes grey from the weather, just the colour of an old fence rail. The trees continue to stand for a good many years, and give this grey colour to the mountain side. Gradually the roots rot, and one by one the trees fall to the ground. Often they lie across each other, six or eight feet high, and this is the "down timber" which it is so hard to travel through. Sometimes it is even dangerous to pass through a piece of this dead timber. If it has been dead a long time, so that the roots of many of the trees have become rotten and weakened, the trees are easily thrown down by a high wind. I have seen a tall, thick tree pushed over by a mule knocking its pack against it, and in a gale of wind have seen the trees falling all around me. Of course, if one of them fell on a horse it would kill him." By this time the waggon had begun to go down into some low but very rough and barren hills, cut up in every direction by ravines and water-courses. There was no grass and the ground was bare, except for low sage-brush here and there, and the rocks seemed to be bent and twisted. Sometimes a little pointed hill was capped by a great broad slab of stone, or again a narrow ridge was crowned with pinnacles which looked like pyramids or church steeples, or men or animals. It was a queer-looking place, and not like anything that Jack had ever seen before. He asked his uncle about it, and he explained. "These are what the old French trappers of early days used to call _mauvaises terres_--bad lands--because no grass grows on them. The soil is all sand or clay, and very dry. All this country you see was once the bottom of a big bay where the tide rose and fell." "Tide rose and fell, Uncle Will! How could that be? Where did the tide come from? I didn't think that the ocean was within a thousand miles of here;" said Jack. "That is true to-day, Jack," said his uncle; "but the time I am talking about was long, long ago, in what the men who study the earth's history call Jurassic time. No one knows how many years ago it was, but it is safe to say it was millions. In those times the salt ocean, or an arm of it, lay just east of the Rocky Mountains and the water in this bay where we are now was partly fresh and partly salt. Great forests grew here, and strange animals lived among them and fed along the shores of this bay. If we had time to get out and look for them, we could find beaches, where the sand was washed up by the waves, and shells, and the bones of these great animals. A big book could be written about these bad lands here, just as big books have been written about other bad lands."