"To thin to plow"

Twain loved the Mississippi, except when it came through a faucet. The drinking water in St. Louis was, he wrote, “too thick to drink and too thin to plow…. It comes out of the turbulent bank-caving Missouri, and every tumblerful of it holds nearly an acre of land in solution.” Such richness had undoubtedly played a large part in giving St. Louis its taste for beer.

William Everdell The First Moderns, 209.