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28 November 2013

Damerham is located between Cranbourne and Fordingbridge, on the Wiltshire uplands (the Downs) at the very edge of Cranbourne Chase – and not that far from the New Forest. As such, it is not surprising it has become the latest Neolithic complex to excite archaeologists. At http://phys.org/print304757967.html … we have a piece on Damerham after a field survey prompted by aerial photography, which spotted crop marks – the field survey (on a recently ploughed field) was designed to see if there was any evidence of life – and tools and bits and pieces came to light. Geophysical imaging and GPS technology narrowed the point down and excavations have begun, revealing prehistoric earthworks going back, it is thought, to 4000BC.

Digging trenches to find post holes and pits, and especially in the search for the line of prehistoric, or not so prehistoric, ditches, is one feature of excavation archaeologists like to map out in order to get a feel of the site. At Damerham they followed down into what looked like a ditch formation – but it kept on going. Not only that, the material in it consisted of orange sand and a yellow and grey clay, suggesting an origin in silt and a former wet environment. This was a puzzle as they were on a chalk upland where water normally percolated through the porous rock to appear as springs and streams along the edge of the upland zone, or in valleys if the water collected at a hard rock formation, or a layer of clay, or chalk and clay, within the chalk formation. They had stumbled across what geologists call a sink hole (or a swallow hole), where water drops down to a different level and over time erodes the chalk in a V formation – or as a pipe formation. They can be seen in quarries and railway cuttings as brown stains in the white chalk and sink holes are commonly found in Dorset and Hants (as the occurrence at Damerham shows) and in the Chilterns. They are formed by erosion and fill with whatever is above the chalk. In the Chilterns this is usually clay and flints but at Damerham it is clay and sand. The sand, itself, may have a connection with the hard sandstone of the sarsen stones, commonly found buried in the soil or just laying around on the Downs. However, as sand also has a connection with water and is a component of silt it could have nothing to do with the sarsen stones. Go to https://www.bgs.ac.uk/science/landUseAndDevelopment/shallow_geohazards/s…

It would seem the prehistoric inhabitants of Damerham, coming across the sink hole, made use of the sand and clay, and dug out a large portion. The excavators hope the fill that replaced the removed material will hold clues on the environment 6000 years ago.

Note … in some areas, modern water run off and small streams will find their way to a sink hole and continue the process of erosion. Chalk itself, consists of soft and hard formations, and other seams can be mixed with clay, or with gravels and sand. Water will percolae through soft chalk as it is very porous but may be diverted when reaching a harder chalk deposit, or one including clay (and water will be diverted sideways instead of downwards). Chalk streams are rare, as it is normally a dry environment with water seeping out of the spring line (along the escarpment) which is where most villages were established. Hence, there must have been springs or a chalk stream at Damerham as it is surrounded by several other villages. Chalk streams can form in chalk valleys if the geology is right – and this occurs in the Chilterns on occasion, and settlements formed along the length of the streams (even if it may sometimes disappear underground).

Here is an image of a bus – you might call that a sink hole (but more likely an old mine working). Towns like Norwich and Reading are riddled with former workings, where mining for chalk and flints was a major industry up to the 19th century. In other parts of the country it is lost workings of coal mines that present a problem, and in Cornwall there are major problems when it comes to building houses as so many holes were dug in search of tin over the centuries, and never written down or recorded, knowledge of them dying out with the death of the miners concerned.

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