Here's an interesting article found by my friend and railroad historian Richard Palmer, entitled When Salt Was A Substitute for Money. Of course, as I've written earlier, money isn't necessarily coins and bills. Money is always that commodity which people freely trade, knowing that other people will accept it in further trade. People will fluidly switch their idea of "money" from coins and bills to salt, or cigarettes, or stones, or beads, or whatever commodity is most widely accepted. So contrary to the title of the article, salt wasn't a substitute for money. Salt was, for a time, money.