On top of the rock cap there is a 100 meter thick layer of chalk from the youngest Cretaceous and above that 75 metres of limestone from the Danien age, the oldest age of the Tertiary. The surface of the Danien limestone would normally be at a depth of 4-500 metres but the salt horst has pushed it up to the surface of the earth.In this Danien limestone the Caves of Mønsted were dug out.
The Danien limestone consists of the shells of one-celled algae which 60 million years ago were floating in the subtropical sea. When the organisms died their shells sank to the bottom of the sea building a thick layer of calcareous mud. As the layer of mud grew thicker the pressure built up pressing the water through the layer of mud.In this way the limestone originates as a compact and solid rock.In the limestone you will find few larger fossils. The reason is probably that the depositing of the algae happened so quickly that a thick layer of mud was built up which offered no good living conditions to the larger organisms living on the sea floor.