6. Third Sort

The third and last sort of rude produce, of which the price naturally rises in the progress of improvement, is that in which the efficacy of human industry, in augmenting the quantity, is either limited or uncertain. Though the real price of this sort of rude produce, therefore, naturally tends to rise in the progress of improvement, yet, according as different accidents happen to render the efforts of human industry more or less successful in augmenting the quantity, it may happen sometimes even to fall, sometimes to continue the same in very different periods of improvement, and sometimes to rise more or less in the same period.

There are some sorts of rude produce which nature has rendered a kind of appendages to other sorts; so that the quantity of the one which any