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Geology Site Account

A-Z Geological Site Index

The Pinnock Stone, BEDLARS GREEN, Uttlesford District, TL52092051, Potential Local Geological Site

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Site category: Boulders - puddingstone

Site name: The Pinnock Stone

Grid reference: TL 5209 2051

Brief description of site:

A giant boulder of Hertfordshire puddingstone 1.67 metres (5 feet 6 inches) high stands upright in a prominent position on the grass by the farmyard of Harps Farm. It is on private land but clearly visible from the public footpath which passes through the farm. Several small sarsen stones are situated nearby. The boulder was recovered from nearby farmland. It is named after the farmer who's plough was frequently hitting the boulder.

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Detailed description

A giant boulder of Hertfordshire puddingstone 167 x 145 x 80 centimetres in size is situated at Harps Farm, close to the public footpath. It was recovered from farmland in about 2006 on the other side of the M11 motorway (still within Essex) at approx. TL 508 204. Part of the Pinnock Stone consists of sarsen stone (i.e. puddingstone without the pebbles).

Two sarsen stones (the largest 135 x 60 x 30 centimetres in size with root holes), are adjacent to the Pinnock Stone. Three more sarsen stones are situated a short distance away and another sarsen stone can be seen at the corner of a farm building.

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The formation of puddingstone and sarsen stones

About 60 million years ago, shortly after the extinction of the dinosaurs, this boulder was part of a beach of flint pebbles on the coast of a subtropical sea. About 55 million years ago the sea had retreated and the layer of pebbles was situated beneath the soil in a hot, dry climate similar to that of the Kalahari Desert today. During this time the pebbles were cemented together by quartz, forming an incredibly tough layer of rock.

During the Ice Age, about half a million years ago, rivers and glaciers broke up this layer and scattered the fragments over Hertfordshire and Essex. This boulder is one of these fragments and the original flint pebbles can be clearly seen. Puddingstone is so called because the pebbles give it the appearance of a plum pudding. It is usually called Hertfordshire Puddingstone because these boulders are most commonly found in East Hertfordshire. Some puddingstone is very colourful and in Georgian and Victorian times it was often cut and polished to make jewelry and decorative items such as snuff boxes.

Sarsen stones were formed in the same way but consist of hard, silica-cemented sandstone without pebbles.



The Pinnock Stone. Photo: John Redfern

 

Sarsen stone at corner of building at Harps Farm
Sarsen stone at corner of building at Harps Farm
Three sarsen stones near the Pinnock Stone
Three sarsen stones near the Pinnock Stone
Adjacent sarsen stones showing root holes
Adjacent sarsen stones showing root holes
Reverse of Pinnock Stone showing patches of sarsen stone
Reverse of Pinnock Stone showing patches of sarsen stone
The Pinnock Stone and adjacent sarsen stones
The Pinnock Stone and adjacent sarsen stones
The Pinnock Stone
The Pinnock Stone

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