Ruby at the Chocolate Hills...
WIKIPEDIA article http://en.wikipedia.org/wiki/Chocolate_Hills says:
The Chocolate Hills are conical karst hills similar to those seen in the limestone regions of Slovenia and Croatia, except that the Chocolate Hills have no caves.[6] According to the karst theory, "sea level changes and uplift combined with terrestrial erosion and air exposure of biogenic reef regions have given rise to hummocky landscapes that are often impregnated with sinkholes and caves." The Chocolate Hills are considered among the striking examples of this karst topography.[16] The Bungle Bungles in the Purnululu National Park in Western Australia feature similar sedimentary formations.