This represents a case where the generations follow one another so rapidly that there are never two ranks, or generations, in condition to reproduce their kind at once, except in rare individual instances, since all, or nearly all, of the old ones die before the young ones have grown old enough to spawn. If such a state of affairs exists, of course any sudden catastrophe, such as a great and cold storm during the winter, or the covering of the water where they lie for a long period with a sheet of ice, happening to kill all the tender young (and old ones, too, often) in a particular district, will exterminate the breed there; since, even if the older and tougher ones survive this shock, they will not live long enough, or at any rate, will be unable to spawn again, and so start a new generation.[10] The set of young scallops is abundant in shallow water upon the eel-grass flats, which often, as is the case of the Common Flats at Chatham, are exposed at extremely low tides. A severe winter often kills off all the "seed" thus exposed. In this case no spawn is obtained the following summer, causing the suppression of the scallop fishery in that locality for at least a few years, and possibly its permanent extinction. III. _Improvement; restocking Barren Areas._--The scallop industry, unlike the clam and quahaug, offers but little inducement to private enterprise. For successful private culture small bays or coves would be needed, and suitable areas are very scarce. The scallop offers better opportunity for communal culture, _i.e._, by towns. There is but one way now known of artificial propagation for the scallop industry, and that is by transplanting in the fall the abundant set from the exposed places to the deeper water before the seed is killed by the winter. It is merely assisting nature by preventing a natural loss, and in no sense can properly be termed propagation. It is merely a preventive, and money used in this way to preserve the scallops is well expended. Usually the set is abundant, and can be transferred in large numbers. This is the only practical method now known of increasing our scallop supply, though it is hoped in the future that other methods may be devised.