A largely ice-covered, glacially dissected island, 135 mi long and 55 mi wide, lying between Amundsen and Bellingshausen Seas off the NW end of Ellsworth Land. The island is separated from the mainland by peacock Sound, which is occupied by the W portion of Abbot Ice Shelf Discovered by R. Admiral Byrd and members of the USAS in a flight from the Bear, Feb. 27, 1940. Named by Byrd for W. Harris Thurston, New York textile manufacturer, designer of the windproof "Byrd Cloth" and contributor to the expedition. Originally charted as a peninsula, the feature was found to be an island by the USN Bellingshausen Sea Expedition in February 1960.