This dramatic landscape started out as the bed of a shallow tropical sea in the Middle Jurassic period, some 180 million years ago. This sea was teeming with shellfish and corals, now preserved as fossils in the rocks. As time passed, the sea bed turned to layers of sedimentary rock, which have since been forced upward by geological movement to form the Cotswold Hills. The landscape we see today was formed by the erosion of these rocks by wind, water and ice, mainly at the end of the last Ice Age.
The bedrock of the upper reaches of the Common is oolitic limestone. However, the majority of the height of the Cotswold Escarpment is made up of Early Jurassic (liassic) clays and silts. Cleeve is the only area of the Cotswolds where the full sequence of Inferior Oolite rocks can be seen. Two layers, the Philipsiama and the Bourguetia beds, are unique to Cleeve Hill and not visible anywhere else in Britain.
For centuries the limestone has been quarried for building. Different quarries give access to different layers of rock with varying uses. Smooth-grained blocks with few imperfections, such as Lower Freestone, made good building stone. Coarser, rubbly rocks containing many fossils, like Gryphite or Trigonia Grit, were suitable for roads and field walls. These rocks are named after the main fossil found in them, Gryphaea (or devil's toenail) and Trigonia (right), two distinctive species of bivalves.
One of the more unusual geological features of the Common is the presence at the surface of sands and sandstone of the Harford Member. In the 18th and 19th centuries, this fine sand was taken off by donkey for use in the Staffordshire potteries.
The Gloucestershire Geology Trust has excavated several sites to reveal the underlying geological features. There is an interpretation board at Rolling Bank Quarry (left), near the top of the escarpment face along from the Golf Clubhouse and directly behind the 18th tee.
For more on the geology of Cleeve Common, contact the Gloucestershire Geology Trust. The Trust produces a rural geology trail guide to the Common in the 'Gloucestershire Uncovered' series. The assistance of the Trust in preparing this web page is gratefully acknowledged.
You can also read more about the geology of the Cleeve Common SSSI on the Natural England website.