These are US Scott #1446 8-cent postage stamps featuring poet Sidney Lanier, issued in 1972.The stamps feature a monochromatic lavender design and were part of the American Poet series.This specific set appears to be a plate block of four, identifiable by the plate number "33364" on the selvage.
Estimate: $30 - $40
Auction : Stamps, Covers & Signatures: A Worldwide Philatelic and Autograph Sale — Cool Stuff Auctions