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| Crags of Crawshaw Sandstone at the Stannington Ruffs SSSI |
June 2022 proved to be a very interesting month, for the further improvement of my knowledge of the geology of Yorkshire – at West Melton and Wath-upon-Dearne in Rotherham, Otley Chevin in West Yorkshire and around the parish of Hunshelf in Barnsley.
Having further investigated the Greenmoor Rock, which is the sandstone formation that I am most familiar with in Sheffield, my next trip was to the Loxley valley in Sheffield, where the British Geological Survey memoir (1957) describes the Crawshaw Sandstone as forming abrupt cliffs accentuated by landslips, where 24 feet of wedge bedded sandstone overlie 6 feet of silty and sandy mudstone.
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| The description of the Stannington Ruffs SSSI |
Volume 11 of the Geological Conservation Review (1996) further states that these crags, known as Stannington Ruffs - a geological SSSI (Site of Special Scientific Interest) - is the best exposure of mouth-bar deposits at the delta front facies in the Crawshaw Sandstone Formation. I had only seen the Crawshaw Sandstone in situ on a couple of visits to Bole Hill in Crookes, where it is a different facies, formed by transverse bars in low-sinuosity rivers – with the sandstones being much coarser and showing mainly planar cross-bedding.
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| Planar cross-bedding in the Crawshaw Sandstone at Crookes |
Arriving on the No. 81 bus from Sheffield city centre, I followed one of the public footpaths on the printed extract from the 1:25,000 map that I had brought with me, but I soon discovered that this didn’t take me very near to the crags and that the rough, steeply sloping terrain beneath them would not easily be negotiated.
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| The Ordnace Survey map of the area around Stannington Ruffs |
I therefore had to be content with just taking a general set of photos at a distance but, apparently, trough cross-bedding is well developed, forming sets about 1 m thick with gently curved basal erosive surfaces, and there is also some ripple cross-lamination, particularly in the upper beds.
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| The crags at Stannigton Ruffs |
Although was not able to get to the crags, the landslips here have left very many large blocks on the lower slopes, from which it was possible to obtain small samples of the Crawshaw Sandstone from them with my Estwing hammer.
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| A slipped block of Crawshaw Sandstone |
The samples I obtained from these are a light buff and very fine grained sandstone, weathering to a mid brown colour on joint planes and weathered surfaces, with muscovite mica on the well developed bedding planes that can be seen in them.
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| A sample of very fine grained Crawshaw Sandstone |
The Geological Conservation Review also mentions that very patchy outcrops of siltstone occur below the main exposure, but there is no evidence of the Subcrenatum Marine Band which lies just below the Crawshaw Sandstone.
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| Loose blocks of Crawshaw Sandstone |
I didn’t see any evidence of this siltstone but when walking down the path, which in places was very eroded by water that must flow here during periods of heavy rainfall, I encountered other examples of very thinly bedded sandstone with an abundance of muscovite on the bedding planes, whose brown colouration contrasts with the light buff body of the very fine sandstone.
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| Samples of very micaceous Crawshaw Sandstone |
Although I still have a very comprehensive textbook from my university days, which I still refer to from time to time, I have never studied sedimentary petrology in any great depth, or spent time closely examining the sedimentary structures in the various outcrops of Carboniferous sandstone that I have seen in South Yorkshire.
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| Sedimentary Environments and Facies |
The mouth-bar deposits such as those seen at Stannington Ruffs are not normally preserved, being removed either by wave-action, or by the subsequent progradation of the delta; however, the Crawshaw delta appears not have migrated further west than this part of South Yorkshire, and wave-action in the Edale Gulf basin into which it prograded was minimal.
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| A track in Acorn Wood |
In several places, the path through Acorn Hill is in the form of a track that is crudely surfaced and there are the remains of walls in the vicinity, sometimes quite substantial, which made me think that there were once mines or quarries; however, most of the ganister mines and coal pits were dug around Stannington Wood and it is probable that these belong to the rifle range, which first appears on the 1924 Ordnance Survey map along with one old quarry.
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| A section of walling at Acorn Hill |
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