The original book published in 1893 had Dorothy's shoes made of silver. It was written by a William Jennings Bryan type "populist" (prairie socialist) who favored the "free coinage" of silver (a preview of ruinous inflationary monetary polices of 20th century leftists).
Incidentally, William Jennings Bryan, even though he lost the presidency 3 times, should still certainly be considered the grandfather of all that is f***** up in the modern world.