Once long ago, when the Blackfeet Indians dwelt on the Canadian prairies, a poor Indian and his two children, a boy and a girl, were living near the bank of a great river. The children's mother had long been dead and they had long been left to the care of their father. Their father did not think it was right that they should grow up without a woman's kindness, and he decided at last to take another wife. So he went far away to a distant village and there he married a queer woman of another tribe. Soon times grew hard in the North Country, and it was very difficult to get food. The family lived for many days on roots and berries, and often they were very hungry because there was no meat. Now it happened that the woman the man had married was a very wicked witch-woman, who was capable of doing many evil deeds. She had no love for her stepchildren, and she treated them very cruelly. She blamed them for the lack of food in the house, and beating them soundly, she said, "You gluttonous brats; you always eat too much. It is little wonder that we cannot keep the house supplied with food." The man saw his wife's cruelty to the children, but although it made him sad, and at times angry, he did not interfere, for he thought the woman should rule her home.
One night in the early spring, as the man slept, his first wife appeared to him in a dream, and said, "Hang a large spider web across the trail in the forest where the animals pass and you will get plenty of food. But be good to my children. Their cruel stepmother is planning to kill them." And she told him where to look for the magical spider web. The next day the man found the large spider web, and he went far away into the forest and hung it from the trees over the trail where the animals passed. That evening when he went back to the web he found many animals entangled in its meshes, for it had magical power. He killed the animals and brought them home, and that night they had a good fat supper of roast deer meat. Day after day the magical spider web gave him great numbers of rabbits and deer, as the vision of his dead wife had told him in the night, and from that time on the family did not want for food.
But the man's success in hunting only angered his witch-wife. She had now no cause for complaint against the little children, and she could no longer scold them and say that because of them there was no food in the house. Her hatred for them grew stronger each day, and at last she decided to kill them and to kill their father as soon as she could. Their father was going away on the morrow in search of wood to make arrows for his bows, and she thought she would have a good chance to kill them while he was gone. Then she would kill their father when he returned. So she laid her plans. But that night the vision of his first wife came again to the man as he slept, and it said, "Your present wife is a witch-woman. She plans to kill the children to-morrow when you are away, and when you come home she will kill you, too. You must kill her while there is yet time. Remember my little children."
When the man awoke in the morning he was much alarmed because of the story told him by the vision of the night. He no longer trusted his witch-wife and he decided to get rid of her. But he feared she would attack the children before he could prevent it. So when the witch-wife went out to get water from the stream to make breakfast, he gave each of the children a stick, a white stone, and a bunch of soft moss, and he said, "You must run away from here and stay away until I can find you, for you are in great danger. You will find these three things I give you of great use. Throw them behind you if any evil thing pursues you, and they will keep you from harm." The children in great fear at once ran away into the forest. Then the man hung his magical spider web over the door of the house, and sat quietly inside waiting for his wife to come back. In a little while she came home, carrying a pail of water, but she did not see the web with its fine strands hanging across the door, and when she walked into it she was at once entangled in its meshes. She struggled hard to get free, but her head was inside the door while her body was outside, and the web held her fast around the neck. Then the man said, "I know now that you are a cruel witch-woman. You will beat my children no more." With his stone-axe he struck her a mighty blow which completely severed her head from her body. Then he ran from the house as fast as he could and went towards his children, who were watching him not far away.
But the man was not yet done with the cruel witch-woman. As he ran from the house her headless body, freed from the spider web, ran after him, while her severed head, with eyes staring and hair flying, followed the children, sometimes bumping along the ground and sometimes rising through the air. The father thought it would be well to go in a different direction from the children, and he went west, while they went east. The children were very frightened when they saw the horrible head behind them, slowly gaining upon them. Then they remembered their father's magic gifts. When the head was close upon them, they threw their sticks on the ground at their backs and at once a dense forest sprang up between them and their pursuer. The children said, "Now we will rest here for a while, for we are nearly out of breath. The wicked head cannot get through that dense forest." And they sat on the grass and rested.
Soon, however, the pursuing head emerged from the thick trees. The children got up and ran as hard as they could, but close behind them came the severed head, rolling its eyes and gnashing its teeth in a great frenzy, and uttering terrible yells. It was very near to them, when the children again remembered their father's gifts. They threw the white stones behind them, and at once a high mountain of white rock rose between them and their enemy. They sat on the ground and rested, and said, "Oh dear, oh dear, what shall we do? We have only one means of safety left, these little bits of moss." The wicked head hurled itself against the mountain, but it could not get through. A big buffalo bull was feeding on the grass near it, and the head called to him to break a road through the mountain. The bull rushed at the mountain with all his force, but the mountain was so hard that it broke his head and he fell down dead. Some moles were playing in the soft earth near by, and the head called to them to make a passage through the hill. So the moles searched and found a soft earthy place in the midst of the rock and soon they tunnelled a hole to the other side of the mountain, through which the head was able to pass. When the children saw their pursuer coming out of the moles' tunnel they cried loudly and ran away as fast as they could. At last, after a very long chase, the head was almost upon them, and they decided to use their last means of protection. They threw the wet moss behind them, and at once a long black swamp appeared where the moss had fallen, between them and their wicked follower. The head was going at such a great speed, bumping over the ground, that it could not stop. It rolled into the swamp and disappeared into the soft mud and was never seen again.
The children then went home to wait for their father. It was a long journey, for they had run far. But their father never came. Months and months they waited, but he did not come, and they grew up to be great magicians and very powerful among their tribe. At last, by their magic power, they learned what had happened to their father. Their stepmother's body continued to follow him as he ran towards the west. It followed him for many days. Then by his magic power, which the vision of his dead wife had brought to him, he changed himself into the Sun, and went to live with his wife in the sky-country. But the old witch-woman also had magic power, and she changed herself into the Moon and followed him to the land of the stars. And there she still pursues him. And while he keeps ahead of her and she cannot catch him, night follows day in all the world. But if she overtakes him she will kill him, and day will disappear and night shall reign for evermore upon the earth. And the Blackfeet of the plains pray that he will always keep in front in the race with his former witch-wife, so that there may be always Night and Day in succession in all the land.
http://english.skazk.ru/catalog/canada-folktales/the-cruel-stepmother-753/