A sixth part of the gross produce may be reckoned the average rent of the tin mines of Cornwall the most fertile that are known in the world, as we are told by the Reverend Mr. Borlace, vice-warden of the stannaries. Some, he says, afford more, and some do not afford so much. A sixth part of the gross produce is the rent, too, of several very fertile lead mines in Scotland.

In the silver mines of Peru, we are told by Frezier and Ulloa, the proprietor frequently exacts no other acknowledgment from the undertaker of the mine, but that he will grind the ore at his mill, paying him the ordinary multure or price of grinding. Till 1736, indeed, the tax of the King of Spain amounted to one-fifth of the standard silver, which till then might be considered as the real rent of the greater part of the silver mines of Peru, the richest which have been known in the world.