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Regarding map symbols, does anyone know when the use of hachures
('tadpoles') was introduced or became common for representing earthworks?
 
In the North East of England, a range of maps and plans prior to the first
edition Ordnance Survey maps (c.1860s) does not seem to show their use.
Larger scale OS maps do use them (if not all that often) in the first and
second series and later.
 
Purely out of curiousity.