When there is an archaeological find, earth has to be carefully removed to expose buried artefacts or building structures. Excluding nearby volcanic disasters, what causes a site to fill up with rubble and debris over time? Where does it come from?
• Your correspondent will find Charles Darwin’s book about earthworms, On the Formation of Vegetable Mould, both interesting and instructive. Earthworms – as well as ants, termites and other such creatures – like to remove soil from beneath objects and deposit it on the surface, so things gradually move downward.
In the past, people made their homes of mud and sticks (wattle and daub), and built defensive walls and major buildings out of mud bricks which, of course, dissolved into more dirt. Middle-Eastern tells are hills formed by the breakdown of mud bricks and mud walls.
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Terry Marsh, Auckland, New Zealand
• Anyone who has a neglected paved area in their garden can see the process of burial begin, as the grass creeps over and creates a new organic layer above. Leaf mould and animal excreta accumulate on top, as burrowing animals from worms to moles and badgers create tunnels below, which slowly subside.
When trees die, larger roots create voids as they rot, causing further subsidence of artefacts. In certain areas, other processes add to the burial. Old settlements were often near rivers in flat areas that periodically flood, so new silt would be deposited on top. If the area remains inhabited, later residents may build there, dispose of ash, food refuse, other rubbish and rubble from old buildings in the area.
Even burial of bodies can raise the land level, which is why many old cemeteries are now above surrounding ground level. This is how the tells or mounds of Middle-Eastern ancient cities built up, and how London’s Roman remains are below current ground level.
Hillary Shaw, Newport, Shropshire, UK
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