ripple marks
柯林斯词典
1. N one of a series of small wavy ridges of sand formed by waves on a beach, by a current in a sandy riverbed, or by wind on land: sometimes found fossilized on bedding planes of sedimentary rock 波痕
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1. N one of a series of small wavy ridges of sand formed by waves on a beach, by a current in a sandy riverbed, or by wind on land: sometimes found fossilized on bedding planes of sedimentary rock 波痕