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clearance cairn
A Clearance Cairn is an irregular and unstructured collection of fieldstones which have been removed from arable land or pasture to allow for more effective agriculture and collected into a usually low mound or cairn. Commonly of Bronze Age origins, these cairns may be part of a cairnfield (a collection of closely spaced cairns) where some cairns might be funerary.〔(Keys to the Past Glossary. )〕〔(English Heritage Dictionary )〕 Clearance cairns are a worldwide phenomenon wherever organised agriculture has been practised.〔(Clearance cairns in Palestine. )〕
== Purpose of clearance ==
By removing large and moderate size stones from the surface and sub-surface, ploughing can take place with much less potential damage taking place to the plough blade. Stones also prevent the growth of plants where they physically block access to the soil and their removal allows for a greater surface area for crops to grow and to allow for plants to grow to their full potential; Stones also increase drainage and may therefore deprive plants of moisture. Stones were removed from fields to allow for the efficient use of hand tools, animal powered machines on such fields in the past and for tractors, etc. in more recent times. Some prehistoric clearance cairns may also contain burials.〔(Warwickshire Time Trail )〕 A few clearance cairns may have been additionally created as boundary markers.〔(The Cairns of Dartmoor )〕 As ploughing developed and specialised the greater depth tilled and the increased power of mechanised ploughing resulted in more and larger stones being brought to the surface and these too had to be removed.
Field clearance cairns sometimes survive long after cleared fields have fallen out of use and are often the only surviving evidence of past agricultural activity in areas of woodland, upland areas, etc. The existence of these cairns was once regarded as suggesting pastoral farming, many now consider them the result of arable or mixed agricultural exploitation enabling ploughing or hand tillage to work more efficiently.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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