The main ‘building material’ of Moravský kras is limestone. During the Middle and Upper Devonian period (370 – 345 million years ago) this area was covered by a shallow, warm sea which provided optimal conditions for the growth and development of massive colonies of living organisms such as corals and stromatopores. The calcareous bodies of these organisms became the main stone of which Moravský kras is built. Calcareous sedimentation finished here during the Early Carboniferous period (345 – 325 million years ago) when the vario-coloured nodular limestone of the Křtiny member were laid down, and which now fringes the limestone belt along the east of the area, especially around Křtiny and Jedovnice. During the Jurassic and Early Cretaceous periods (167 – 100 million years ago), when the climate here was tropical, a cockpit-type karst area formed on the Rudické and Babické plošiny plateaux with deep depressions and the remains of tropical karst cones. Terrain irregularities were filled with minerals of the Rudice layer. The quartz geodes are interesting for mineralogists. We can also find a notable representation of fossil types, such as ammonites, belemnites, echinoids and sponges. During the Paleogene period, from 65 to 25 million years ago, a new karst cycle began linked with the development of karst valleys and the first stage of the cave system development. During the Neogene period, from 25 to 1.8 million years ago, the valleys were deepened into canyon-like valleys and the cave level continued to develop. During the Pleistocene (1.8 – 0.01 million years ago), and especially its early part, frost weathering, the formation of flowstone formations and accumulation of Quaternary sediments was typical. By this time the cave network had developed to the approximate extent that we can see in Moravský kras today.