Everything in Yolngu country belongs to one of two halves. Dhuwa and Yirritja divide people, clans, land, water, songs, designs, ceremonies and the plants and animals themselves, and the division is not a classification laid over the world afterward but the structure the world is understood to have. A person is born into the father's half and must marry into the other, so the two halves are permanently dependent on each other for the continuation of both, and a ceremony belonging to one half requires people of the other to conduct parts of it. A clan's songs, its designs and its stretch of country are its own property, held and transmitted by named people, so that a design painted on bark or on a body is title to that country as much as it is decoration. That last point explains why Yolngu religion has an unusual public record.
In 1963, when the Commonwealth excised part of the Arnhem Land reserve for bauxite mining without consulting the people whose country it was, Yolngu leaders at Yirrkala sent the House of Representatives a petition typed in Gumatj and in English and mounted on painted bark, using the clan designs as the statement of ownership they already were. The Yirrkala bark petitions are now held among the founding documents of Australian democracy. The Gove land rights case that followed in 1971 put the Yolngu religious relationship to country before an Australian court, which found against them, and in doing so made the argument for legislation instead.