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van Veen, J. (author)Where the top layer of clayey substance was thin and the underlying peat layer thick, the shrinkage of the latter had been such that the clay-filled gullies appeared as ridges of about ½ to 1 m high in the field. Farmers sometimes call these ridges ,,natural dykes". In some places they have dug up parts of these ancient depots of good clay and...report 1942