This image depicts a region 20 million years ago which is now known as Sturgeon Bay of the Great Lakes. You will notice much white powder covering the surface. This terrain is heavily imbedded with the mineral lime. During this time there were long periods of moisture and very cool temperatures. This condition produced the effect of 'effloresence'. To 'effloresce' is to cause the lime to 'bloom'. This effect is the loss of water through evaporation causing crystallization upon exposure to the air so that the lime would turn to a white powdery substance on the surface. We all see this condition during late winter and early spring on concrete, bricks and natural stone. Many thanks to christianfly for the Clearwater, UT DEM file; and, to Dotthy for the wonderful .atm and .srf files of her picture: Reef. Rendered at 6000 x 4500. Render time: 47.5 hours for a 4097 x 4097 terrain.