A ripple-marked grainstone bed in the upper Hemse Beds is described externally and internally. Most of the ripple-mark crests are flat, and some are concave. The entire surface is covered by traces, most of which are biogenic. It is concluded that the ripple train was generated by oscillatory wave action, and that the flat and concave crests were caused by penecontemporaneous erosion. A reconstruction of the original ripple form is made and the mean grain size is estimated. A graph is constructed which enables an interpretation of the set of ripple-marks in terms of wave conditions and absolute water depth. It is concluded that the ripples were formed by waves with a period of about 11 s and a near-bottom water-particle orbital diameter of about 0.9 m, at a water depth of about 10 m or less.