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 Rev. 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. If there had been no tax, this fifth would naturally have belonged to the landlord, and many mines might have been wrought which could not then be wrought, because they could not afford this tax. The tax of the duke of Cornwall upon tin is supposed to amount to more than five percent or one-twentieth part of the value; and whatever may be his proportion, it would naturally too belong to the proprietor of the mine, if tin was duty free. But if you add one-twentieth to one-sixth, you will find that the whole average rent of the tin mines of Cornwall, was to the whole average rent of the silver mines of Peru, as thirteen to twelve. But the silver mines of Peru are not now able to pay even this low rent, and the tax upon silver was, in 1736, reduced from one-fifth to one-tenth. Even this tax upon silver too gives more temptation to smuggling than the tax of one-twentieth upon tin; and smuggling must be much easier in the precious than in the bulky commodity. The tax of the king of Spain accordingly is said to be very ill paid, and that of the duke of Cornwall very well. Rent, therefore, it is probable, makes a greater part of the price of tin at the most fertile tin mines, than it does of silver at the most fertile