Ancient history The Wren's Nest National Nature Reserve is world-famous geologically for its well-preserved
Silurian coral reef fossils. Considered the most diverse and abundant fossil site in the British Isles, more than 700 types of fossil have been found at the site, 86 of which are unique to the location, including
Calymene blumenbachii, a
trilobite nicknamed the
Dudley Bug or
Dudley Locust by 18th century quarrymen. An image of this trilobite featured on the town's coat of arms until 1974. During the height of the Industrial Revolution, up to 20,000 tons of limestone was quarried annually. In 2004, Wren's Nest and the nearby
Castle Hill were declared Scheduled Ancient Monuments, as they represented the best surviving remains of the limestone industry in
Dudley. The most impressive part of this is the last remaining surface opening limestone cavern in the world – formerly reaching more than 100 metres underground – which is known as the Seven Sisters. The workings were originally connected by underground canal to the
Dudley Tunnel complex, which has now been blocked off for safety reasons. The Wren's Nest's geological value was first recognised by
Sir Roderick Murchison in 1839, and now both the ex-quarry and the tunnels are visited by scientists from all over the world to study its valuable content. ==The Seven Sisters tunnel complex==