group of islands lying off the northwestern coast of Queensland, Australia, in the Gulf of Carpentaria. Sighted in 1644 by the Dutch navigator Abel Tasman (Tasman, Abel Janszoon), they were charted (1802–03) by the British navigator Matthew Flinders and named in honour of Marquess Wellesley (Richard Colley Wellesley), then governor-general of India. The islands are generally rocky or sandy and are covered with scrub and fringing mangrove forests. They are divided into two groups. Mornington, the largest (250 square miles 【648 square km】), is the northernmost. Lying 15 miles (24 km) offshore, it rises to 300 feet (90 m) and has a mission station for Aborigines and an airport. Bentinck (59 square miles) and Sweers (6 square miles) are the largest of the southern islands.