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| An outcrop of the Cadeby Formation on Main Street |
For the past few years, I have taken advantage of the Heritage Open Days festival, which is now held over two weekends in September and for my next day out, following my investigation of the geology in Whirlow and Ecclesall Woods, I decided to visit St. Leonard’s church in Scarcliffe – a village to the south-east of Bolsover in Derbyshire, which is 20 km from Treeton as the crow flies.
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| The locations of Treeton, Palterton and Scarcliffe |
The 53a bus from Sheffield to Mansfield only runs every two hours but, as I had discovered when visiting the mediaeval churches in Bolsover and Barlborough, for the return journey it is possible to get a more regular bus to Chesterfield and then catch the X17 to Sheffield.
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| Palterton and Scarcliffe |
To fit in with the afternoon opening of St. Leonard’s church, my plan was to firstly visit the nearby hamlet of Palterton, set on the edge of the Magnesian Limestone escarpment, which I had first visited back in 1993 when undertaking work for English Heritage at Bolsover Castle and Sutton Scarsdale Hall, before walking the short distance to Scarcliffe.
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| An outcrop of the Cadeby Formation on Main Street |
At the time, although still living in London and having very little knowledge about the Magnesian Limestone, I had been very curious about the small but very distinctive outcrop of reddened rock at the southern end of Main Street.
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| The Cadeby Formation on Main Street |
Having lived in South Yorkshire since 1997, however, I have since surveyed very many quarried and natural exposures in the Cadeby Formation, as well as many historic buildings made out of it - from Knaresborough in the north to Nottingham in the south - and when rubbing it with my fingertips, I assumed that it must be one of the sandy varieties, but I didn’t examine it with my hand lens at the time.
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| A detail of the Cadeby Formation on Main Street |
The British Geological Survey memoir for the region cites a silica content in the Cadeby Formation of 25% around Scarcliffe and in the Mansfield area, where it forms the greater part of the formation, it contains 50% silica and is properly described as a dolomitic sandstone.
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| A detail of the Cadeby Formation |
The largest outcrop at the junction of Main Street and Rylah Hill is composed of thin beds of very irregular thickness, which have low angle cross-bedding in places, undulating surfaces and are sometimes quite contorted.
Looking at the geological map, there is a transition from the dolomitic limestone of the Cadeby Formation to calcareous mudstone, formerly known as the Lower Permian Marl, which in the field is seen as an increase in the thickness and the frequency of mudstones downwards and a gradual passage into the lowermost strata.
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| A yellow/mottled variety of the Cadeby Formation |
The colour of the sandy limestone here is predominantly red, although there are mottled and yellowish variations within the L-shaped outcrop, which is no more than 100 metres in length from one end to the other and is interrupted by the entrances to a couple of houses.
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| Thin flaggy beds in the Cadeby Formation |
Although I didn’t see any exposures of calcareous mudstone, at the north end of the principal outcrop, the strata described above are overlain by very thinly bedded flaggy limestone, which has very low angle cross-bedding.
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| A specimen of red granular dolomitic limestone (21mm coin) |
From the main outcrop, I collected a couple of samples of the red limestone and a small piece of yellowish limestone. I had initially thought the rough texture of the samples was due to a high sand content but, when viewing them through a hand lens, the texture is actually produced by dark pink grains of dolomite, with some having distinct rhombohedral crystal faces.
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| A specimen of pink/red granular dolomitic limestone (21mm coin) |
I can gouge a small pit into the surface with the tip of my steel knife, with the resulting very fine powder reacting very positively to hydrochloric acid – suggesting that the sand content is not very high; however, it is at times like this that I would benefit from having a petrological microscope or a powerful binocular microscope to properly see the mineral components.
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| A specimen of yellow/pink dolomitic limestone (21mm coin) |
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