Geology Site Account

Site name: Wintry Wood Brick Pit (disused), next to Brickfield Business Centre, in the Lower Forest, north of Epping.

Grid reference: TL 469 035

Brief description of site: Disused and overgrown brickworks pit in Wintry Wood. The pit presents an ideal opportunity to create a small section in Anglian boulder clay (till) which is not exposed or available to study elsewhere in Essex.

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Summary of the geological interest:

About 450,000 years ago, during the coldest part of the Ice Age, Essex was situated at the southern edge of the Anglian Ice Sheet. The ice sheet was up to 2 kilometres (over a mile) thick in places, and covered most of Britain. Its extent is fairly well known because it has left behind evidence of its existence in the form of a rock called boulder clay, or till (often referred to as Anglian till). The ice sheet extended as far south as Chigwell and Hornchurch and so north of this line can be found deposits of boulder clay except where it has been removed by erosion.

Wintry Wood Brick Pit is a former brickworks pit in the Lower Forest, which worked boulder clay. It has been disused since 1895 and is very overgrown but boulder clay can still be seen in one or two places in the sides of the pit. The site is on public access land and is part of Epping Forest. It is the only publicly accessible place where you can see direct evidence for the former existence of glaciers in Essex.

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Scientific interest and site importance

As the ice moved it ground up and carried along pieces of the rocks over which it passed, just as glaciers and ice sheets do today, and when the ice melted an unsorted clayey residue called boulder clay, or till, was left behind. Most boulder clay was probably laid down or lodged at the base of the moving ice sheet as the immense pressure caused the ice to melt; it is therefore sometimes referred to as lodgement till. Boulder clay contains rocks transported long distances by the ice and known as glacial erratics. By matching rock types with known outcrops in other parts of Britain geologists are able to establish the direction of ice movement across the country from its origins in Scotland or Scandinavia. Many erratics show scratches that were received when the rocks passed over each other at the base of the ice sheet.

The composition of boulder clay varies according to the rocks over which the ice passed. In Essex the boulder clay usually contains a lot of chalk picked up as the ice passed over the chalk hills of Cambridgeshire, Suffolk and north-west Essex. The exposure in Wintry Wood Brick Pit shows typical Essex chalky boulder clay, which consists of chalk fragments and flints in a matrix of grey clay. However, the clay in the upper part is usually weathered to a brown colour. The clay content of the boulder clay is mostly derived from the Jurassic clays of Cambridgeshire and the East Midlands and it often contains Jurassic fossils, also brought south by the ice. Typical fossils include belemnites from the Oxford Clay and the bivalve Gryphaea (also known as the Devils toenail) from the Lower Lias. The chalk fragments are usually well-rounded and often have flat surfaces with striations caused when they were lodged at the base of the ice sheet and the ice, containing other rocks, passed over them.

The pit was part of Wintry Park Brick and Tile Works, which was in existence by 1838 but had closed by 1895 (Ryan 1999). Whitaker (1889) briefly refers to this pit when describing exposures of boulder clay in London area, stating: œBy the kiln on the north of Epping Plain there was a good section€. Boulder clay in this area is usually decalcified and free of chalk in the uppermost 0.5 to 1.3 metres (Millward et al. 1987) and that seems also to have been the case here.

Based on a borehole at Thornwood, to the north, the boulder clay here is probably 5 to 6 metres thick and overlies the much older Claygate Beds of Eocene age. Various erratic pebbles and cobbles can be found around the sides of the pit. Some are from the boulder clay but others may have been washed down from the older Stanmore Gravel (formerly called Pebble Gravel), which overlies the Claygate Beds about 150 metres to the south.

Wintry Wood Brick Pit is currently the only publicly accessible place in Essex where Anglian till can be seen and examined. It exposes typical Essex chalky boulder clay, which is direct evidence of the existence of the Anglian Ice Sheet. It is therefore of considerable educational value.

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Other information

There is a layby almost opposite the pit. Public parking is also available off The Woodyard south of the B181 Epping Road (TL 472 030).

Wintry Wood Brick Pit. Photo: G. Lucy