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| A bed of conglomerate in the Mexborough Rock at Darfield Quarry |
The day after an afternoon spent in Sheffield, to explore the Upper Carboniferous rocks exposed along Hartley Brook Dike, I went to Darfield with my next neighbour Dan, who grew up in the village He wanted to show me around Darfield Quarry, in the Mexborough Rock, which I had briefly visited back in 1996 when surveying potential RIGS (Regionally Important Geological Sites) in Barnsley.
After taking a quick walk around the churchyard at All Saints church, which I had visited during the Heritage Open Days festival in 2019 - to photograph the grave of Ebenezer Elliott – Dan drove to Balkley Lane, from which we approached the quarry and descended a set of steps made of large blocks of stone into the railway cutting, which disorientated me.
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| An exposure of Mexborough Rock in the railway cutting |
On my previous visit, I had entered the disused railway line at the west side of the old Mill Houses Bridge on Doncaster Road and had continued until I had found a few quarry faces, where I saw a conglomeratic bed that was full of clay ironstone nodules. I had also noted this distinctive feature in the Rotherham Red variety of this sandstone formation at Boston Park in Rotherham, which is now completely overgrown with ivy.
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| An exposure of Mexborough Rock in the railway cutting |
When preparing my “Let’s talk about the stones” walk, I had read a short article on the Sheffield Area Geology Trust (SAGT) website, which reported on the discovery of an ‘omelette structure’ at Boston Park and that SAGT were looking for evidence of a flood event.
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| An 'omelette structure' in the Mexborough Rock at Boston Park |
At the time of the original RIGS surveys in South Yorkshire, I was using colour transparency film to record my observations and, although I haven’t yet been able to scan and share them in a digital format, these would probably help to prove this hypothesis.
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| Concentrations of ironstone on the joint planes |
On one of the quarry faces, the joint planes display dense concentrations of ironstone that look quite purple in colour, which I thought was quite unusual, but I couldn’t find the place where I had seen the conglomeratic bed.
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| Massive sandstone passing upwards to flaggy beds |
In the same quarry face, the transition from thick massive beds in the lower parts to flaggy beds with cross-bedding in the upper section can also be clearly seen. This reflects the change of the flow regime within the river channel that deposited the sediment and, as I have noticed in many other places, the flaggy beds are highlighted by the surface weathering processes.
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| Stone carvings in Darfield Quarry |
When wandering around the quarry, I was surprised to see that numerous faces and other relief sculptures had been cut into the quarry face, which have been undertaken here and elsewhere in Barnsley by Melvin Dickinson and Billy Johnson.
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| A stone carving |
Eventually, I eventually found a bed in a quarry face that is obviously severely deformed, compared to the massive sandstone above and below it. Although the sediment has not been overturned here, as at Boston Park, it is a reasonable assumption that it relates to the same flood event.
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| A deformed bed within the massive sandstone |
Following this bed laterally, which reaches 20-25 cm in thickness, it is seen to contain a concentration of large clay ironstone pebbles, which can also be seen as isolated nodules in the overlying massive sandstone.
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| A conglomeratic bed with ironstone nodules |
Having succeeded in my objective of finding an exposure of this conglomerate, albeit in a different location to where I originally noted it, I took a set of record photographs that I can share if needed but, with SAGT not responding to my comments that I made about Darfield Quarry after I had seen the ‘omelette structure’, I am just content to have satisfied my curiosity about this.
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| A detail of ironstone nodules in the conglomeratic bed |
One interesting feature that I didn’t notice at the time is that, although most of the clay ironstone nodules are like those seen in the Rotherham Red sandstone, a large rounded clast seems to be a bedded sandstone that has been presumably been reworked from a consolidated deposit.
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| A large clast of reworked sandstone |
It was less than 2 hours since we had first arrived in Darfield, but it had been a very enjoyable afternoon out in the sunshine and, once I had collected a few specimens to add to my growing rock collection, we headed back to Dan’s truck and set off back to Treeton.
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| Rocks collected from Darfield Quarry |
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