Geology Site Account

Site name: St. Barnabas Church, Alphamstone (churchyard boulders)

Grid reference: TL 8787 3546

Brief description of site: Large number of sarsen stones in the churchyard. One of the best places to examine these erratic boulders in Essex.

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Summary of the geological interest

Alphamstone churchyard contains a remarkable number of large boulders, some over a metre long. There is even a boulder inside the church. These stones are known as glacial erratics and were carried to Essex by the Anglian ice sheet which covered almost the whole of Britain during the coldest period of the Ice Age, some 450,000 years ago.

The boulders are known as sarsens, an extremely hard sandstone formed around 55 million years ago when the climate of Britain was hot and a layer of sand beneath the surface of the ground became cemented with quartz. They are thus very resistant to erosion and have survived the rigours of the Ice Age. These stones probably originated on the chalk downland of south Cambridgeshire and after retreat of the ice they became concentrated in river valleys such as The Stour.

The abundance of sarsens here suggests that a former Pagan stone circle may have existed on this site, all the stones being transported here by man. The stones may be partly responsible for the name of the village.

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Scientific interest and site importance

Sarsens are not uncommon in this part of Essex but nowhere else in the county are so many concentrated in one place. The sarsens of Alphamstone have been referred to in books and articles on the landscape and history of Essex (eg. Rudge 1964) and archaeological reports (e.g. Hedges 1980). All the stones are rounded and water-worn and typical of sarsens elsewhere in the Stour valley.

There are at least 11 sarsens here; 10 in the churchyard and one inside the church (at the base of the west wall of the nave). At least two stones have almost disappeared beneath the grass and it is likely that there are others in the churchyard that are now completely buried. It is understood that there are sarsens in private gardens elsewhere in the village which may have come from the churchyard.

The formation of silcretes (which includes sarsens) has been the subject of recent scientific debate. Research has compared the conditions under which sarsens were formed with the present day climate in the Kalahari Desert and parts of Australia.

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Other information

The stones are of historic interest. They link geology, archaeology and social history. It is obvious that they have been moved by man to their present position but when and why this was done is not known. It is likely that the present church was built on a Pagan site of great antiquity which may have been a circle of stones. To gather such a collection in one spot it would probably have been necessary to move some stones several miles. St. Barnabas church is mostly fourteenth century with Norman origins.

The fourteenth century church of St. Barnabas, Alphamstone. Photo: W.H. George