For the Warnumamalya - the 'True People', the Anindilyakwa name for themselves - the clans and their estates were established during the Dreaming, amutiyurrariya, and charged with a spiritual essence, mardayan, that endures. The Barabara clan estate includes Chasm Island, a place of deep importance to all who live on Groote Eylandt. One narrative tells how three beings shaped these waters: the Baler-shells called Yukana, the dolphins Amatuana, and the tiger-shark Bangudja. A Baler-shell family camped on Bickerton Island, then moved north to Chasm Island, where they lived joyfully alongside a pair of dolphins, gathering food and playing in the warm shallows - until the violent Bangudja killed the Dolphin-man. The grieving Dolphin-woman turned herself into a long coastal boulder; her companions became a striking stone column at the island's summit. On a cliff face, a red stain marks where Bangudja struck, and at low tide the form of the slain Dolphin-man still shows above the water.

Between 5 and 14 January 1803, Matthew Flinders charted the coast aboard the Investigator, sailing around Groote Eylandt and landing on this small island to take bearings. He gave it the name that stuck: the deep chasms splitting the cliffs - crevices running roughly southwest to northeast, crossed by others north to south - made it hard to climb. The island covers about 3.2 square kilometres of flat but broken country, rising to seventy-nine metres. Flinders, ever the naturalist, noted its close-grained sandstone studded with quartz, and a strange apple-sized fruit, sharp to the taste, that he took for a new species. He was recording a place that the people of Groote Eylandt had known intimately for thousands of years.

In the chasm caves, Flinders found what he called 'rude drawings, made with charcoal and something like red paint upon the white ground of the rock' - porpoises, a turtle, kangaroos, a human hand. He sent the expedition's artist, William Westall, to copy them. Westall's two watercolours are the earliest known European documentation of Australian rock art, and Flinders wrote what amounts to the first site report. One painting showed a kangaroo followed by a file of thirty-two figures, one of them twice the others' height and holding a weapon - a leader, the Englishmen guessed. We should be clear about whose work this was: not Flinders', and not Westall's. They were visitors copying the art of Anindilyakwa people, an art whose makers had their own names, their own law, and their own reasons, none of which the strangers were equipped to read.

Most of the paintings are maritime - men in canoes with spears and paddles, a hunter with a harpooned turtle, shoals of fish, a water goanna - the record of a saltwater people describing their own world. In 1948, the American-Australian Scientific Expedition to Arnhem Land returned to trace and photograph the art, and the archaeologist Frederick McCarthy charted how its styles had shifted over a very long span: from early outlines to linear designs to pecked engravings, changes that likely tracked deeper shifts in belief and ceremony. McCarthy's careful methods marked a turning point for Australian rock-art research. Today the island is protected, and access is strictly controlled by the Anindilyakwa Land Council - a fitting arrangement for a gallery that was never abandoned, only waiting to be understood on its makers' terms.