cliff. In estuaries and other suitable places, primary and secondary marsh 

 may develop side by side. 



Mangrove swamps are a special kind of salt marsh. The mangroves may 

 be accompanied by other plants or grasses. Their intricate root systems bring 

 about the deposition of quantities of silt and this is also aided by the other plants. 

 In places the decay of the mangrove roots leads to the formation of a dense peat. 

 The zoning of mangroves may be as clearly marked as that of plants on a salt 

 marsh in temperate climates. The close interrelation of mangroves, mud 

 deposition, and shingle ridges or coral reefs and similar habitats is well illus- 

 trated in the island-reefs of the Queensland coast and in the cays and shingle 

 islands around Jamaica. 



There is yet another reason why salt marshes are so interesting from the 

 physical point of view; the rates of growth and change are usually much quicker 

 in them than in most other natural features. Even in a few years, extensive 

 alterations can be mapped, since the marshes are rising steadily and spreading 

 outwards, although at the same time parts of them may be cut back by erosion, 

 and secondary marsh may develop in front of a small erosion cliff. Growth 

 and erosion are, however, intimately associated with the plants that thrive on 

 the marshes, so that it is virtually impossible to separate ecological from 

 physiographical processes in the study of marsh evolution. Moreover, most 

 marsh areas are adjacent to dunes and shingle ridges. Wind-blown sand and 

 wave -moved shingle may be spread over a marsh, and there are few, if any, 

 better localities in which to study the way in which sediment of all degrees of 

 coarseness may be mixed. 



DISCUSSION 



Redfield: I would like to make two comments that came to my mind. One, 



as you talked, 1 was very much impressed by how different your 

 English marshes are from our New England marshes and these 

 marshes here (Georgia). Superficially your marshes look much 

 more like our marshes on the West Coast. 1 think that is for 

 botanical reasons. I get the impression that everything is hap- 

 pening on a much shorter time schedule. On the other hand the 

 principles that you brought out are perfectly identical. For ex- 

 ample the growth of the creeks: your conclusion is exactly the 

 same as 1 have arrived at. Naively, from looking at our own 

 New England marshes there is just one other point that I would 

 like to make. You commented on the geographical influence, the 

 character of the hinterland and that sort of thing, and also the 

 temperature of the climate. I would like to raise a question as 

 to whether also the moisture characteristics of the climate and 

 the details of the tidal regime are not extremely important. 

 Obviously the range of tides, the mean range, is very evident, 

 but my impression, on looking at the West Coast marshes a 

 year ago was that these were marshes the surface of which dries 



