Wren’s Nest derives its name, not from breeding birds, but from the Old English word Wrosne, meaning “the link”. This may relate to its topographical position on the boundary between the Severn and Trent watersheds.
Wren's Nest is a classic geological site of exceptional importance, being one of the most notable geological locations in the British Isles and visited and studied by geologists from all over the world.
About 420 million years ago, tropical seas covered the area where Dudley now stands, with coral reefs inhabited by trilobites, crinoids (sea lilies), brachiopods and many other creatures. Their remains may be found today as perfectly preserved fossils in the limestone rocks at Wren's Nest, collections of which occur in museums throughout the world. Over 700 types of fossil are known from Wren's Nest, 186 of which were first discovered and described here, and 86 are found nowhere else on Earth.
Wren's Nest was declared as the UK’s first National Nature Reserve for geology, in 1956, in recognition of its exceptional geological and palaeontological features. The site provides a definitive section through the Much Wenlock Limestone formation.
Around 1837, Sir Roderick Murchison spent some years studying fossiliferous rocks in the Midlands. He visited Dudley on a number of occasions and, in 1839, published his scientific work 'The Silurian System', establishing this major time period in Earth history. About 65% of the fossils illustrated and described are from Dudley, and many of the individual specimens used are housed in the collection at Dudley Museum.
Wren's Nest played an important part in the very development of the Black Country, not least because Abraham Darby, Father of the Industrial Revolution, was born on Wren's Nest in 1678. Dud Dudley (son of Lord Dudley) had, by 1665, developed a process to smelt iron with coke instead of charcoal, but local charcoal burners, who feared that their livelihoods might be threatened, destroyed his furnaces. Darby developed Dudley’s work and perfected the process in Coalbrookdale by 1709.
For centuries the limestone was quarried for building stone and for use as an agricultural fertiliser. Huge quantities were excavated during the industrial revolution to act as a blast furnace flux in the Black Country's iron and steel industry, leaving Wren's Nest honeycombed by caverns and underground workings. The caverns known as the Seven Sisters are the spectacular openings to the workings, which formerly descended 100 metres below the hill.
During the height of the Industrial Revolution, up to 20,000 tons of limestone were removed annually to act as a flux in the many local blast furnaces. This activity ceased in 1924, leaving the area honeycombed with great quarries and caverns, some going down 100 metres below the hill to underground canal basins. However, the site would never have been so well exposed without such excavations and few would have known the history of the rocks. It was during this period that many of the best fossils were found, the most famous being the Trilobites. One of these, Calymene Blumenbachii, was so common that is became nicknamed the 'Dudley Bug' and featured on the town's Coat of Arms until 1974.
When the quarrying and mining ceased, the hill was abandoned and left to nature. It is now colonised by grassland, scrub and Ash-Elm woodland. The limestone rocks support plants that are adapted to lime, including county rarities such as Autumn Gentian, Small Scabious, Common Gromwell and Bee Orchid. The woodlands are home to birds like Sparrowhawk, Stock Dove, Tawny Owl, Green and Great Spotted Woodpeckers, and Nuthatch; the caverns offer important roost sites for several species of Bat, whilst the locally uncommon White-letter Hairstreak butterfly survives on the elms.
A major roof collapse occurred in October 2001, which, if left unchecked, would have resulted in the loss of the Seven Sisters. A project co-ordinated by the Geotechnics team secured funding from English Partnerships Land Stabilisation Programme to fill in the lower caverns and to temporarily fill the upper daylight gallery with stone to protect it from further collapse. The project was accepted as a Demonstration Project in the ODPM Constructing Excellence scheme and achieved the maximum score under the Considerate Constructor Scheme. Further feasibility studies are being commissioned to consider the best ways to stabilise the Seven Sisters and to realise the tourism potential of the site.
In October 2004, Wren’s Nest and Castle Hill were declared a Scheduled Ancient Monument in recognition of them having the best surviving remains of the limestone quarrying, mining and processing industry in Dudley. This includes the last remaining surface opening limestone cavern in the world – the Seven Sisters.