Geological nature reserves

Cornwall Wildlife Trust has two geological nature reserves in Cornwall, St Erth Pits Nature Reserve and Tresayes Quarry Nature Reserve. Many of CWT's nature reserves (there are over fifty) have some geological interest: an example is the flagship Helman Tor Reserve (see image above, by Ilaria Selvaggio / Selvaic).

Geological nature reserves are sites that have been acquired or leased by Cornwall Wildlife Trust and are important for geological and biological reasons. They illustrate the close links that exist between the geology of an area and its wildlife habitats.

St Erth Pits Nature Reserve

St Erth Pits were originally worked for moulding sand and clay of Pliocene age. The St Erth Pits Nature Reserve is of national importance and this is recognised by its designation as a Site of Special Scientific Interest (SSSI). It provides evidence of the climate and geography of this part of west Cornwall some two million years ago when the sea level was about 45m higher than today and the sea water was slightly warmer. An information board about the site can be found on the wall of the Star Inn in the village of St Erth and a St Erth Pits Nature Reserve information leaflet is also available. The moulding sand was used by Harvey's of Hayle, and the clay was used for puddling the dry-dock in Penzance in 1834, and also by Bernard Leach who had his pottery in St Ives in the 20th century. Well-preserved fossil molluscs, foraminifera and ostracods were found in the clay, as well as plant material. The microfossil fauna is particularly diverse, reflecting the range of habitats from brackish to open marine. Only one of the pits at St Erth is now a CWT reserve - and only sand is found in it, and much of that is probably spoil. The Turritella gastropods in the clay beds are typically 5-7cm long while the ostracods and foraminifera are much smaller (e.g. Leptocythere sp - an ostracod - typically 0.4-0.8mm. There are fossils from St Erth on display in the Royal Cornwall Museum, Truro).