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Whin Sill erratic at Leven

By Colin Howes and Mike Horne

During the Yorkshire Naturalists' Union VC63 meeting to Leven on 25 June 2022, Colin Howes of the Doncaster Natural History Society noticed a large brown, rectangular, domed, water-worn boulder embedded in the grass verge of South Parade, adjacent to the frontage of the fine brick built early 19th century Grade II Listed Building named Westfield House (TA 103453). In this Hull valley landscape with no exposed solid geology or underlying strata which could have produced this rock type, this incongruous object, unless brought by human agency, seemed likely to be an ‘Erratic’ brought by glacial action during the Quaternary ice ages.

Whin Sill erratic at Leven

Visual inspection showed the boulder to be a medium grained basic igneous rock and the most likely name would be ‘Whin Sill’, a dolerite from northern England. To obtain a more accurate identification a geologist would need to remove a sample to see an unweathered surface and make a thin section. Even then it is not always possible to link the erratic to its original source. Some erratics are readily identifiable and come from a single locality, such as Shap Granite and Larvikite, for others the identification has to remain more generic.

Whin Sill erratic

It is probably not in its original position and was probably moved there to protect the corner of the house from vehicle damage. There are several large quarries (some disused and some still active) in the area around Leven extracting glacial and post-glacial deposits. 

Whin Sill, formerly referred to as Whinstone, has a specific geographical distribution in the northern Pennines from Teesdale to Berwick in the Scottish borders where it forms the basis of such celebrated landscape features as High Force, High Cup Nick and Lindisfarne and is the elevated topographical feature on which Hadrian’s Wall was built.

At the end of the Carboniferous and the beginning of the Permian geological periods (about 301-294 million years ago), tectonic plate movements (the Variscan orogeny) created four surges (swarms) of volcanic activity intruding magma between existing rock strata and erupting at surface via fissures. On cooling it solidified into the tough crystalline doloritic rock referred to as Whin Sill. Since quite large boulders of Whin Sill feature in the glacial boulder clays of Holderness and east Yorkshire, examples in North Cave (SE8932) and Cottingham (TA0432) being used as curb stones (Anon, 1894), it is likely its occurrence in Leven is similarly via glacial progression from the north.

Recording, mapping and identifying glacial erratics became popular with the Yorkshire Naturalists’ Union and its affiliated societies in the late 19th century, the YNU forming The Yorkshire Boulder Committee to organise this work which reported in the YNU Transactions and The Naturalist from 1894 to 1905. Also The East Yorkshire Boulder Committee of the Hull Geological Society reported in their Transactions from 1893 to 1909 and Humberside Geologist 1987 to 2021. By this means it has been possible to trace the origins and routes of glaciers across Ice Age Yorkshire.

In Hornsea a similar but larger boulder of Whin Sill, first recognised by W.H. Crofts (Anon, 1896) who described it as dolerite, achieved celebrity in 2009 when its scientific and cultural significance was established by the Hull Geological Society and local community action. Now referred to as the Hornsea Tesco Boulder,  it was repositioned through the generosity of the nearby TESCO store in a landscaped plot of its own, accompanied by a stainless steel information panel and unveiled to the public with civic/corporate pomp in 2012 (Haughey et al, 2020).

Until now, the presence of the Leven boulder seems to have evaded academic notice, though whether it has generated any local folklore is yet to be discovered. During the YNU excursion, having seen examples of Leven’s landscape features and historic and vernacular architecture, the boulder at over 290 million years of age, is likely to be by far the oldest object in the locality.

 Note - a version of this article was originally published in The Naturalist.


Anon. 1894 Report of the East Riding Boulder Committee 1893-94. Transactions of the Hull Geological Society. 1: 6-8.#

Anon. 1896 Report of the East Riding Boulder Committee 1896. Transactions of the Hull Geological Society. 3: 6-9.

Haughey D, M Horne and S Jones 2020. The Hornsea Tesco Boulder. Humberside Geologist Online no 16.

Howes C & M Horne 2022. Geological field note: 'Whin Sill' erratic in Leven village. The Naturalist 147, p 197.


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