Imbricate structures in conglomerate. Diagram showing prominent imbrication of platy fragments along the top of a gravel layer in Pennsylvanian Wamsutta clastics near Attleboro, eastern Massachusetts. It is to be noted that the bases of the gravel layers are relatively even because the first pebbles to be rolled in place traveled over the smooth surfaces made by the underlying sand. Flat pebbles like those showing conspicuous imbrication can be rolled along the bottom easily if turned so as to behave as upright disks in the current. When they fall over, they are likely to assume an imbricate relationship: for this is the most stable under conditions of strong bottom currents. Shrock, 1948, p. 255.