The Wealth of Nations by Part 4 Chapter 7 Page 75

to render herself as much as possible independent, not only of Sweden, but of all the other northern powers, Great Britain gave a bounty upon the importation of naval stores from America, and the effect of this bounty was to raise the price of timber in America much more than the confinement to the home market could lower it; and as both regulations were enacted at the same time, their joint effect was rather to encourage than to discourage the clearing of land in America.

Though pig and bar iron too have been put among the enumerated commodities, yet as, when imported from America, they were exempted from considerable duties to which they are subject when imported from any other country, the one part of the regulation contributes more to encourage the erection of furnaces in America than the other to discourage it.