Potsdam sandstone, sedimentary rock, Cambrian, deposited 500 million years ago. The Potsdam, or Nepean sandstone is found at Inverary, near Kingston. It was laid down in the Cambrian Period. The sandstone shows typical sedimentary features such as ripple marks, low closely - spaced ridges created in sand by the action of waves or currents. Cross bedding layers of sand accumulated at an angle to the bedding. Sandstone pillar columnar structures are also found in the sandstone.