Geology Site Account

Site name: Harlow Puddingstone

Grid reference: TL43200898

Brief description of site:

A giant boulder of Hertfordshire puddingstone that was originally inside the private quadrangle of the offices of Glaxo SmithKline (formerly BP House) in Third Avenue.

Following demolition of the buildings the stone is now outside GSK.'s grounds, outside its main gates, in an open access green space which has been landscaped.

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Site description

A large boulder of Hertfordshire puddingstone 1.65 metres (5 feet 6 inches) high formerly stood upright in the private quadrangle of the offices of Glaxo SmithKline (formerly BP House) in Third Avenue. It was discovered during construction of the building in 1966. Following demolition of the buildings the stone is now outside GSK.'s grounds, outside its main gates, in an open access green space.

Hertfordshire Puddingstone is an extremely hard rock with an interesting history.

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.

The Harlow Puddingstone in its original position in the quadrangle of GSK offices. Following demolition of the building it has now been relocated outside the main gates. Photo © G. Lucy