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Grimes Graves flint mines
north-east of Brandon, Norfolk, UK
associated engineer
Not known
date  circa 2500 BC
era  Pre-Roman  |  category  Mining/Quarrying  |  reference  TL816898
ICE reference number  HEW 472
East of Weeting, some 11km from Thetford, are several hundred flint mines thought to date from the late Stone Age and very early Bronze Age. The mines are collectively known as Grimes Graves and this is the largest group of Neolithic flint mines in Britain. Grass or trees cover most of the shafts. One pit is open to the public.
Stone was the most important and widely used material in prehistoric engineering, and remained so for many centuries, even after the technological revolution heralded by the introduction of metals. Flint was prized in particular because it is a hard but workable material suitable for making tools and weapons. Flint nodules, having a glass-like fracture quality, can be 'knapped' (chipped) to give a razor-sharp cutting edge.
The Grimes Graves site covers more than 30 hectares along the slopes of a shallow valley. Depressions in the ground surface reveal that 700-800 pits were dug, of which over 400 survive. Worked-out pits were backfilled with spoil from the next pit along — new shafts were sunk every one or two years.
The geology here consists of sand and boulder clay above chalk. There are three bands of flint within the chalk strata, known as topstone, wallstone and floorstone. The finest flint nodules (black, shiny and easily flaked) come from the deepest layer, the floorstone. They are less flawed and more durable than flints from the upper layers or those found on the surface.
Miners dug funnel-shaped pits down to the chalk level and then sank vertical shafts through the chalk to the floorstone. The configuration of each mine varies slightly, depending on the depth of the flint layer being worked.
The deepest of the shafts is about 12.2m and the diameters vary between 4m and 7.9m. In some shafts the hard chalk has been undercut to form a bell-shaped cavern for working the flint vein. Radiating galleries were cut from the shafts at floorstone level to extract as much flint as possible. The galleries formed a network of tunnels between adjacent shafts.
The wide pits would have been lit by natural daylight but the passageways were excavated using light from small lamps with floating wicks, made by filling hollows in the chalk walls with animal fat or oil. Soot marks can still be seen on the roofs of the galleries.
Beds of stone chips on the surface indicate that the flint was knapped in situ to form axe heads and other cutting tools.
The engineering significance of Grimes Graves is demonstrated by the practical knowledge of soil mechanics displayed by the Neolithic miners and in the tools they used. They adopted the technique of battering the excavation at the angle of repose, through the softer soil. Their mining tools were picks made from the antlers of red deer and shovels made from wood or animal shoulder blade bones. These have been assessed as being about 70 percent as efficient as modern equivalents.
Archaeologist and clergyman Canon William Greenwell (1820-1918) excavated one of the shafts in 1868-70 and deduced correctly that the landscape was the result of Neolithic flint mining. He found antler picks and a stone axe made of Cornish greenstone.
Further archaeological excavations were carried out in the 1970s — by Roger Mercer in 1971-2 for the Department of the Environment, and by the British Museum in 1972-6. Radio-carbon dating at Greenwell’s pit showed that it had been in use between 2580 and 2400 BC. There is also evidence for some mining extending into the Bronze Age. Radio-carbon dating of other artefacts from the site show that the area was being mined between 2330 and 1740 BC.
Pit No.1 (Greenwell’s pit, TL817898) is open to the public. It is about 9m deep and 7.6m diameter top and bottom, narrowing to 4m wide in the middle. This gives the top 3m of silt, sand and clay a proper angle of repose, with vertical sides through the 4m depth of chalk between the two upper flint layers, and then undercutting in the hard chalk from 2.1m above the floorstone layer of flint. The pit has 27 galleries, with nine main headings about 1.5m high.
Grimes Graves is a Scheduled Ancient Monument and occupies a Site of Special Scientific Interest. It is one of only 10 Neolithic flint mines known in England, of which six survive as earthworks.
Research: ECPK
"Great sites: Grimes Graves" by Peter Topping
in British Archaeology, Issue 72, York, September 2003
reference sources   CEH E&C

Grimes Graves flint mines