Summary of site:
This is a famous fossil locality containing a rich fauna from the Ashgill epoch, the last major time division of the Ordovician period.
The Killey Bridge Formation is seen in only limited exposures and excavations in the area but in total is believed to be around 250 m thick. It consists largely of siltstones, mudstones, flagstones and a 3 m thick sandstone. Some of these rocks weather into rottonstones where the fossil is completely etched away leaving almost perfect natural moulds. All the rocks are fossiliferous. The well-preserved fauna is diverse and includes brachiopods (lampshells), trilobites, bivalve molluscs, sea snails, nautiloids with simple conical shells, corals, bryozoa (moss animals) and the graptolite Dicellograptus anceps which dates the formation precisely. Graptolites were an enigmatic group of rapidly evolving colonial marine animals living in simple tubular structures attached to floats. They appeared at the start of the Ordovician period and became extinct during the Devonian. Because they floated everywhere they had widespread distribution and their rapid evolution meant they were restricted to relatively brief time intervals. This makes them ideal fossils for dating the rocks that enclose them.
The Killey Bridge formation was formed on a shallow, inshore sea bed 443 million years ago on the south east margin of a supercontinent called Laurentia (including present day North America, Greenland and the northern half of the British Isles) imperceptibly drifting northwards towards the equator.
This locality gives a precious glimpse of a sea bed teeming with some of the first thriving populations of marine organisms and is nationally and internationally important. It is therefore vital to protect the limited exposures and to enhance them if possible.