“But even if there had been no march, the Okies would have been made obsolete by the depression. The histories of depressions show that a period of economic chaos is invariably followed by a period of extremely rigid economic controls – during which all the variables, the only partially controllable factors like commodity speculation, unlimited credit, free marketing, and competitive wages will get shut out.”

Cities In Flight, by James Blish, pages 421-422. From the multi-edition book published by Gollancz. Copyright 1970.

The book has many interesting themes for science fiction fans and interestingly, commodity-based money is a key plot device. The date of the copyright is interesting – it is just a year before Richard Nixon finally severed any link between the dollar and gold, to his everlasting shame.

Here is a nice appreciation of Blish over at "Templeton Gate 3.0".