An educational display piece showing ripple marks in greywacke from Moffat, Scotland. These ripple marks indicate agitation by water or wind (in this case water), these ripples are asymmetrical meaning that the ripples have a gentle up-current slope and a steep down-current slope. Greywacke is a type of dark, hard, grey or brown sandstone . It is typically poorly sorted with angular grains of quartz, feldspar & lithic fragments set in a very fine matrix. It is thought to have been deposited from heavily sediment laidened currents ( turbidity currents ) moving very rapidly downslope through water. This specimen is an ideal educational piece, it weighs roughly 1.179 kg and measures approximately 23 x 18 x 2 cm.