A boulder wall, also spelled boulder-walls or bowlder-wall, is a kind of wall built of round flints and pebbles, laid in a strong mortar. It is used where the sea has a beach cast up, or where there are plenty of flints.
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This article incorporates text from a publication now in the public domain: Chambers, Ephraim, ed. (1728). "Boulder wall". Cyclopædia, or an Universal Dictionary of Arts and Sciences (1st ed.). James and John Knapton, et al.