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Geology & History of Split Rock

The distinctive red limestone on the northern face of Split Rock
The distinctive red limestone on the northern face of Split Rock

The Rock

Getting your head around the geological timescale is baffling but having a grasp of when, as well as how, the rocks we climb on were formed adds a fascinating historical dimension. Though today’s landscape was shaped by ice, rivers and sea within the last two million years (i.e. the very recent past), the rock themselves are far, far older.

Limestone in the caves of Wookey Hole
Limestone in the caves of Wookey Hole

Split Rock Quarry is made of Carboniferous Limestone. This is the same rock that forms the larger part of the Mendip Hills, producing other notable features such as Wookey Hole (just next door), Cheddar Gorge, Burrington Combe and the Avon Gorge. The Mendips have a rich industrial mining history and there are many old sites across the area that are now nature reserves, as well as large active sites still operating. Areas of Carboniferous Limestone can also be found elsewhere in the UK, including much of the south Wales coast and Pembrokeshire (a top destination for climbers).

Limestone is a member of the calcium carbonate family that also includes chalk, dolomite and marble. It’s a sedimentary rock formed from the remains of billions of tiny shells and skeletons of microscopic animals. Limestone is composed mostly of the minerals calcite and aragonite and was formed in Britain between 363 and 325 million years ago. To give some context, the earths continents were still part of one large landmass (Pangea) and the dinosaurs were still a few tens of millions of years away! During this time many of the planets coal-beds were also forming, leading to this era being called the "Carboniferous" period (Latin for "coal-bearing") and hence the term "Carboniferous Limestone" today.

Limestone can vary massively in its appearance around the world, but is commonly white to grey in colour. Limestone that is unusually rich in organic matter can be almost black in colour, while traces of iron or manganese can give limestone an off-white to yellow to red colour. These traces are likely what has produced the stunning deep red rock on the northern wall at Split Rock.

Despite varying in its appearance, limestone is a favourite type of rock for many climbers. Neat and effective footwork helps enormously on limestone, with the handholds and footholds often being small but very reliable. These small crimpy-features can lead to a lot of pressure on the hands and fingers which makes some routes very punishing. But fear not! We have a selection of beginner routes at Split Rock that can get you a taste of outdoor climbing without pushing too hard.

Beginner friendly outdoor climbing!

History of Split Rock

The main quarrying area at Split Rock (known as Underwood Quarry) was opened during the First World War by the Wells Stone Company, who leased the land from Lord Brougham and Vaux.

In 1919 the 12 acre site and plant was sub-leased by the Somerset County Council to support their road building and maintenance activities, paying a royalty to Wells Stone for the rock extracted. Over the next century the quarry was a busy site as the council expanded its presence in the area, opening a railway siding to the Cheddar Valley railway and producing over 300,000 tons of limestone. By the 1950s a precast concrete plant was opened on the site to provide work for when conditions were too wet to work on the quarry face. By the 1970s the quarry was producing a quarter of a million tons per year.

The main quarry face

The site was also the home to the councils Central Repair Depot, which was responsible for the repair of the councils fleet of vehicles. Initially this was steam rollers and steam wagons, but by 1950 the fleet included 371 highways vehicles, 249 fire brigade vehicles, 75 school meals vans and 70 ambulances. After the quarry closed, Thales UK operated a radar signature measurement range for the evaluation of radar signatures of large targets. The range was described as 200 metres wide and 50 metres deep and offered very low external electrical noise interference levels.

Limestone has numerous uses: as a building material, an essential component of concrete (Portland cement), as aggregate for the base of roads, as white pigment or filler in products such as toothpaste or paints, as a chemical feedstock for the production of lime, as a soil conditioner, and as a popular decorative addition to rock gardens. Many local buildings and buildings in the wider area utilised limestone in their construction.



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