Why is the sea salty?

In Denmark there were two millstones that could grind out anything. King Frodi used two strong slave women, called Fenja and Menja, to grind out gold, peace, and prosperity for him. They turned the heavy stones and out those things came, and Frodi ruled over a wealthy and peaceful land.

The women toiled year after year. And over the years the slave women hated King Frodi more and more for making them slaves, especially in a land where everyone else was enjoying freedom and wealth. And so they decided to use the magic millstones for something else. They ground out an army to oppose the king.

Fighting began, and for the first time in an age there was violence and desolation in the land.

The sea king Mysing heard rumours of the civil war and sailed out in his ship, famous for its power and size, and landed in Denmark. Once ashore, he and his warriors carved their way through the armies on both sides until they reached Frodi’s halls, killed the king, and carried off the millstones and the slave women. Fenja and Menja were now no better off than they had been before, and they cursed Mysing even as he put them aboard his ship.

Sailing away from Denmark with his spoils, Mysing told the women to grind out salt.

“Is that all you want?” they asked.

“I really like salt,” he replied.

The women had been grinding out salt for a long time before their prayers were finally answered and a storm came and sank the ship along with the king, the women, the stones, and a ship-load of salt.

And Mysing’s ship was so big that the salt it held was enough to fill the whole sea, and make its waters salty forever.

(I’ve been reading The Prose Edda by Snorri Sturluson.)