Skillogalee Dolomite (age about 750 my)
The importance of grass and acacia seeds as grain for grinding to flour led to substantial demand by Aboriginal groups in the desert for replacement grinding slabs. In some areas, this demand was met by specialised grindstone quarries, which fed finely finished millstones into the long-distance exchange networks snaking across the interior. The most striking concentration of these millstone quarries is in the southern part of the Lake Eyre basin, where there are at least 10 quarries including major complex at Anna Creek, Tooths Nob and Innamincka.
The Anna Creek quarry is known to Arabana-Wankangurru people as Palthirri-pirdi (lit. millstone [palthirri] quarry [pirdi]). Mythologically, this long narrow outcrop of fine-grained grey-white sandstone, 200 m long, is said to represent a fish bone. In geological terms, it is a Neoproterozoic sandstone, a minor part of the basal member of the Skillogalee Dolomite. The slabs were dug out of the outcrop in a series of shallow pits to reach the unweathered sandstone, roughly shaped by flaking to thin the slabs and to rough out an oval shape, and then finely finished by hammer-dressing to create elliptical slabs up to 50 cm long.
Quarrying activity at Anna Creek was clearly intensive as numerous quarry pits crater the outcrop. In 1897, Thomas Worsnop calculated that 1354 t of stone (1032 m3) had been excavated from the main part of the quarry, which he estimated represented the production of about 71,000 millstones (he allowed for 25% wastage, and used field observations which showed the largest millstones measuring 46 x 30 x 8 cm). Worsnop only dealt with part of the quarry, and as the quarry pits extend along the entire length of the outcrop, the actual production rate of millstones may have been 3--4 times this figure, perhaps around 200,000 millstones.
The full extent of trade in this stone is yet to be established. Field surveys and oral accounts point to a wide distribution of Anna Creek grindstones across the southern part of the Simpson Desert, especially in the Kallakoopah Creek area, and possibly also into the Mann-Musgrave Ranges (where the well-known Ngintaka Dreaming refers to attempts by Pitjantjatjara people to negotiate access to the trade in millstones from the east).
The development of Aboriginal economies, based on native grain as a staple food, around 3000--4000 years ago, and the major expansion of seed-grinding and processing within the last millennium, required the provisioning of large areas of sandy desert with grinding slabs. The large-scale production of grinding slabs in the Lake Eyre basin, alone represents production of perhaps 1--2 million millstones over the life of these quarries. And within this economy, Palthirri-pirdi with its fine white sandstone was a major centre of production.
Mike Smith, National Museum of Australia and Australian National University
Caption: The famous Anna Creek (Palthirri-pirdi) millstone quarry showing some of the quarry pits and other workings. Credit: Colin MacDonald.
Further information: For further information on the Lake Eyre basin quarries, see M. Smith ‘The archaeology of Australia’s deserts’ (2013).