The Wealth of Nations by Part 4 Chapter 5 Page 42

It would appear, therefore, that it is principally foreign salt that is used in the fisheries. Upon every barrel of herrings exported there is, besides, a bounty of 2s. 8d., and more than two-thirds of the buss caught herrings are exported. Put all these things together and you will find that, during these eleven years, every barrel of buss caught herrings, cured with Scotch salt when exported, has cost government L1 7s.

5 3/4d.; and when entered for home consumption 14s. 3 3/4d.; and that every barrel cured with foreign salt, when exported, has cost government L1 7s. 5 3/4d.; and when entered for home consumption L1. 3s. 9 3/4d. The price of a barrel of good merchantable herrings runs from seventeen and eighteen to four and five and twenty shillings, about a guinea at an average.