EPICONTINENTAL SEDIMENTATION 495 



higher concentration of suspended mud in the tidal flat area than 

 is found in the open sea, without loss of sediment taking place. 

 In this respect freshwater added to the tidal water behaves quite 

 differently because it cannot settle out. In a few tidal cycles it is 

 dissipated and lost to the open sea. 



The mechanisms described lead to a gradual decrease in medium 

 diameter of the bottom sediment as one passes from the inlets 

 toward the watersheds and coasts, and to a gradual accumulation 

 of mud in the area. However, a different phenomenon occasions 

 loss, namely the effect of storms. These churn up the mud, and the 

 ebb current carries a large amount back to the sea. This happens 

 on the largest scale when the storm drives exceptional quantities 

 of water in at the windward inlets, across the watersheds, and 

 flushes it out again through the leeward passages. 



The general conditions do not change noticeably in the course 

 of a few years so that roughly speaking the gradual accumulation 

 and the spasmodic losses appear to balance each other. Whether 

 there is secular storage or slow waste in the course of a number 

 of years will depend on variations in supply, climate, changes of 

 sea level, biological activity, and human intervention. Because 

 of the huge amounts of sediment that have to be handled by the 

 currents if they are to bring about a general rise or depression of 

 the average bottom surface, many years must elapse before it is 

 possible to recognize any tendency. The sense of any such tendency 

 may be reversed before it has been possible to detect it. 



This brief review of the storage of clay in tidal flat regions shows 

 that it is evidently necessary to take into account animal and 

 plant activities, physicochemical behavior of clay particles, tidal 

 current systems, wave action, storm surges, laws of particle set- 

 tling, compaction, suspension, measurement of grain size, and 

 accurate charting. One even has to reckon with changes in climate 

 and of sea level if quantitative assessments are envisaged. 



In conclusion I should like to point out that the moral of this 

 paper is obvious: oceanology is more than the sum of its component 

 branches. We are members of a team. 



