Recent drilling by the South Australian Department of Mines south of the Mount Toondina piercement structure, encountered a Devonian dolomite – anhydrite sequence below 2,925 feet. The Upper Devonian is overlain, probably with slight unconformity, by 375 feet of Permo-Carboniferous sandstone, conglomerate and shale, 855 feet of Sakmarian marine shale and siltstone and 1080 feet of Artinskian freshwater siltstone, sand and coal beds. The uppermost 615 feet consist of Mesozoic sediments. Drill stem tests conducted over porous intervals in the Devonian and in the basal Permo-Carboniferous indicated excellent reservoir properties of the sediments tested, and recovered slightly gas-cut salt water with strong traces of methane and higher hydrocarbons. Reconnaissance seismograph surveys carried out by the Department indicate the presence of up to 6000 feet of Palaeozoic section in both the Arckaringa Sub-Basin and the Boorthanna Trough. The discovery of a Devonian evaporate sequence in the Arckaringa Sub-Basin throws new light on the Middle-Palaeozoic palaeogeography, and upgrades the petroleum potential of an area comprising some 5,600 square miles which has barely been touched by petroleum exploration.