Gypsum rocks are sedimentary rocks made up of sulfate mineral. In the Triassic period, vast lakes formed in the desert, and as the water evaporated, layers of gypsum were deposited. At the time, East Devon was located towards the edge of a vast basin, and Portland lay towards the middle of it. Over 100 metres of salt were deposited in the same layers.
Find out more on the rocks and pseudofossils pages.