We know from fossils found there that the limestone from Wren’s Nest was formed in a shallow tropical sea around 425 million years ago and the purest beds of the limestone (called the Upper and Lower Quarried Limestone Members by geologists) can be burnt to produce high quality lime.

A fossil hunting trip to the Wren Nest, Dudley

Lime is in demand today as it is used in the restoration of older buildings, where the use of Portland cement is not suitable.

More information on the event can be found here.

The Black Country is an area located just to the northwest of Birmingham right at the heart of the UK. It includes the towns of Dudley, Walsall and Wolverhampton and is noted for its industrial past. It is so named because of the concentration of mining, iron production and metal working in the area. There is significant evidence for the Black Country to lay claim to be the home of the industrial revolution. The earliest reference to mass iron production in the Black Country is a factory located in Wednesbury during the 1400’s. American visitor, Elihu Burritt was so impressed with what he saw in 1869 he said “The Black County, black by day and red by night, cannot be matched for vast and varied production by any other space of equal radius on the surface of the globe.”

This legacy began back in 1598 with the birth of Dud Dudley, son of the Earl of Dudley. Dud attended Balliol College, part of Oxford University until his father’s business was struck by financial troubles. He then returned home to help run his father’s foundry. History was then made by the discovery of coal as a successful fuel to smelt iron, rather than the dwindling supply of charcoal fuels due to the timber being used for ship production. His success led to a patent from the King around 1620 for the process used in the factory located at Pensnett Chase, near Himley Hall in Dudley. Dud produced a record 7 tonnes of iron per week. This process was later developed and refined by Abraham Darby who was born at Wrens Nest Manor in 1678. Abraham had a factory in Coalbrookdale in 1709 and used coke as a fuel.

What is now left of the Lower Quarried Limestone after the mines closed

Dudley’s limestone has been mined for centuries for use as an agricultural fertilizer amongst many other uses. The Black Country continued its influence on industrial developments as limestone was discovered to be a very successful flux in the iron smelting process. For this reason, the Wrens Nest limestone mines produced up to 20,000 tonnes annually. The mines extend thousands of metres underground and formed a honeycomb network of caverns supported by huge pillars of rock. Dudley’s mine supporting rock pillars are unusual as a majority do not support vertically but are inclined, and some are almost horizontal due to the near vertical dip of the rocks known as the Much Wenlock Limestone Formation in certain areas. Many of the underground mines are connected by canals, and the only way to enter the caverns at the present is by canal barge since many of the original entrance shafts have been sealed up. The canals were the main transport route for the coal and limestone, they linked the mines to the furnaces. Many of the early canals were only created to allow passage for the heavy coal traffic.

The final limestone was excavated from the Wrens Nest in 1924. As a result the mines have been left for nature to dominate once more. The Seven Sisters daylight gallery is an open air mine which has been stabilised with tonnes of an intrusive igneous dolerite hardcore, but many of the underground mines have collapsed as the last miners robbed the final supporting pillars during their retreat. 70 meters beneath the Wrens Nest National Nature Reserve is the Step Shaft mine, adjacent to the largest unsupported underground canal basin in the UK. In the basin there are original 200 years old timbers, nails, plateway rails and even cart wheels which are extremely well preserved due to the wet, low oxygen environment. Cathedral cavern and the Minstrel Gallery (South workings of Wrens Nest East Mine) adjacent to the canal basin were in filled with sand in 2009 to prevent the walls collapsing and losing this spectacular cavern. It is claimed to be large enough to fit the volume of St Paul’s cathedral inside, this is certainly the case for the larger Dark Cavern. In the future the aim is to reopen Cathedral Cavern as part of the Strata Project, which will allow visitors to explore our hidden past through a visitor attraction allowing access to these underground wonders via canal boats and underground lifts, providing the funding can be found one day.

Step Shaft Canal Basin below the Wrens Nest, photo by G. Worton

Chris Broughton
Geologist
Wolverhampton Art Gallery