Monday, 21 February 2022

The Chatsworth Grit at Wyming Brook

Wyming Brook

In the first week of June 2021, having spent the previous Sunday exploring the Sheffield Board Schools in Netherthorpe, Crookesmoor and Broomhill and the geomorphology in this part of Sheffield, my next day out was to Wyming Brook.
Wyming Brook and the Rivelin Dams

Located just inside the Peak District National Park, on the south side of the Rivelin Valley, I became aware of it when looking for places to visit during the summer, after researching the Carbrook Ravine Nature Reserve on the Sheffield and Rotherham Wildlife Trust website.
The Rivelin Valley is not a part of Sheffield that I know well, having only visited the Rivelin Rocks to look at the Chatsworth Grit when surveying the RIGS (Regionally Important Geological Sites) in the Peak District National Park and visiting the Rivelin Glen Quarry in 1995, with a short walk along part of the Rivelin Valley Trail in 2014.
The clock tower and 'Oak Sculpture'
Alighting at the terminus of the No. 51 bus from Sheffield at Lodge Moor, before heading west along Redmires Road, I was curious about the clock tower that was once part of the Lodge Moor Hospital, initially built following the smallpox epidemic of 1887-1888, and was delighted to see the stainless steel ‘Oak Sculpture’ by Mike Johnson.
A ridge of the Rough Rock seen from Redmires Road

On the approach to the head of Wyming Brook, to the south of Redmires Road, the topography is seen to rise in steps, which marks the position of the Rough Rock, a coarse grained sandstone that forms part of the uppermost formation in the Millstone Grit Group.
The path leading to the stepping stones at Wyming Brook

Taking the first available path down to Wyming Brook, the steep slope contains many small blocks of gritstone embedded in rock debris and soil, which form a deposit known as head and leads to a relatively open and flat area of ground, where stepping stones cross the brook.
An 'edge' formed of Chatsworth Grit

Following the path alongside the brook, after a short distance the stream gradient steepens noticeably, with the Chatsworth Grit on the opposite bank forming a distinct ‘edge’ and, hoping to obtain my first sample of this very coarse sandstone, I crossed the footbridge with my Estwing 20 oz brick hammer in hand.
An outcrop of Chatsworth Grit

As I had discovered during one of my geological field trips at Nottingham University, when examining the granite tors of the Cornubian Batholith in Cornwall and Devon, where there are no obvious ledges or angles, it is not very easy to break off the rock from massive outcrops like this.
Small samples of coarse grained Chatsworth Grit

Having found a place where I could chip off a small piece, the coarse grained sample that I obtained was very weathered – a result of the deterioration of the mineral microcline feldspar in the gritstone. This constitutes a considerable proportion of the very coarse deltaic sandstones that were derived from granitic highlands, which lay to the north during the Carboniferous Period.
Blocks of Chatsworth Grit in Wyming Brook

Making my way further downstream, the brook passes through a block field, consisting of large slipped blocks of gritstone, similar to those seen along the eastern boundary of the Peak District National Park, as at Burbage Edge, where Burbage Brook passes down through Padley Gorge.
A view of the block field at Wyming Brook

In many places, the muddy path has been laid with roughly square or rectangular blocks, but for much of the way from the top to the bottom of the course of the brook, I had to walk over blocks and natural rock debris that in places weren’t easy to traverse - especially where springs were emanating from the slopes above the brook.
A spring flowing across the path

Sometimes, the gradient of the brook lessens to form pools, where the rock fragments in them are stained with orange iron oxides and hydroxides, which are derived from the Chatsworth Grit - a characteristic of most of the Upper Carboniferous sandstones in South Yorkshire.
Iron staining in the stream bed

From start to finish, where I took the path heading west past the Rivelin Dams, I had walked less than 800 metres down quite a steep sided wooded valley, but with a descent of 100 metres and all along the way, large slipped blocks litter the surrounding slopes.
A wooded slope with slipped blocks

Apart from providing an excellent example of the erosional and depositional features associated with the Chatsworth Grit edges, it must be the most spectacular landscape that I have encountered to date during my exploration of South Yorkshire.
A large slipped block of Chatsworth Grit

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