Dark earth

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This article is about the archaeological horizon. For other uses, see Black earth (disambiguation).

Dark earth in archaeology is an archaeological horizon, as much as 1 m (2 – 3 ft) thick, indicating settlement over long periods of time.

In England, dark earth notably seals remains of Roman date, particularly so in urban locations. In the example of London, deposits underlying the ancient city's dark earth are often dated to between the 2nd to 5th century AD, with overlying deposits frequently dated to the 9th century. The dark earth shows little evidence of any depositional structure or 'horizons', although tip lines are sometimes recorded.

In Sweden, dark earth covering 40 hectares has been found in Uppåkra (in southernmost Sweden, former Denmark), where city-like settlement existed from about the year 1 until 1000 C.E. when the settlement shifted to modern day Lund. Dark earth over 7 hectares has been found in the Viking city of Björkö (today called Birka), in central Sweden, close to modern Stockholm. Dark earth has also been found in Köpingsvik, on the island of Öland close to the southern Sweden east coast.

The material is high in organic matter, including charcoal, which gives it its characteristic dark colour; it may also contain fragments of pottery, tile, animal bone and other artefacts. In some cases, it may represent open spaces on the edge of urban centres, but can also be found in more rural settings in and around foci of settlement. In London, it has been taken as evidence of the decline of Londinium's population or of its partial displacement outside the city walls. London's soil, London Clay, is naturally very impermeable and unsuitable for agriculture without improvement.[1]

Some archaeologists see dark earth as reworked urban stratigraphy, indicating timber, smoke-impregnated thatch, decayed weeds, and earth floors reworked by worm action.[2] They argue that late Roman cemeteries around London do not show a population decline compared with earlier London. More recent "reworked stratigraphy" ideas are based on theories that abandoned soils were reworked by agricultural action, such as ploughing, which mixed building materials from the abandoned Roman cities into stratigraphy higher up the sequence.

In the Hebrides, it was customary to remove the thatch from the "black houses" every spring, and spread it on the fields as fertilizer, improved by the soot which it retained. On Achill Island, special smoke huts were built in the fields, stone structures with sod roofs. From October to May smoky fires burned inside them, and in spring the sods were spread on the fields.[3]

Dark earth was originally called 'black earth' by archaeologists in London. Because of confusion with the chernozem (black earth soils in Russia) (where the dark colour comes from humus, not soot), it was renamed dark earth.

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Notes[edit]

  1. ^ View of the Agriculture of Middlesex: With Observations on the Means of Its Improvement, and Several Essays on Agriculture in General. By Board of Agriculture (Great Britain), John Middleton. Published by G. and W. Nicol, second edition, 1807. Page 20.
  2. ^ Darwin on earthworms
  3. ^ The book of masonry stoves. David Lyle. Brick House Publishing Co, Inc. Andover, Massachusetts, 1984. ISBN 0-931790-57-3 (paperback edition) p.23

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