Proposed theories concerning the nature and mode of formation of limestone scallops are examined. Some progress is made toward a purely theoretical understanding. Scallop formation is simulated by generation on blocks of Plaster of Paris in a laboratory flume under known and controlled conditions and the relationships between the resulting features, the generating conditions and the base material examined. Field Evidence both confirms these relationships and reveals other unsuspected factors. The similarity between these features and others found on ablating snow surfaces is investigated and the same laws found to apply.