larger levees of sand accumulate at the margin. The sediment within is finer 

 and is poorly drained, while the grass is less vigorous and may die off in the 

 least drained areas. The thickness of peat is greatest in the central area and 

 extends below the level where the Spartina grows at the margin. 



With increasing size and elevation, a concentric drainage system is form- 

 ed by small creeks which converge to form a central trunk which emerges at 

 some point in the marginal levee. Coarse sand is found drifting into these creeks 

 from the surrounding flats. Along the margins of these creeks levees are found 

 on which Spartina grows vigorously. The enclosed areas are muddy and fre - 

 quently bare, in spite of being well above the low^er limit of growth on the sur- 

 rounding margins of the island. The peat in the central areas may descent 30 

 inches below this present limit. See Figure 12. 



No transition has been found between this type of marsh structure and the 

 high marsh. In no case do the marsh islands rise to within 30 inches of the 

 level of high marsh. It seems possible that the higher islands represent an 

 equilibrium condition beyond which development cannot proceed under present 

 conditions . 



The features described above are interpreted as steps in a progressive 

 development of the marsh. There is also evidence that destructive processes 

 have taken place on a large scale. The entire high marsh, fronting the open 

 harbor and extending into the larger creeks, terminates in "banks" which are 

 unquestionably the result of erosion. In exposed situations the peat rises ver- 

 tically for a height of seven feet above the low water line and large masses of 

 peat recently broken off are in evidence. 



Wherever examined the peat in these banks is found to be stratified: two 

 or three feet of brown fibrous material overlaying a gray clay -like substratum. 

 Some widespread phenomenon must account for this stratification. A section of 

 an unusually good exposure of the marsh structure is shown in Figure 9 , super- 

 imposed on the diagram in such a way as to suggest that the upper layer is an 

 exposure of high marsh peat and the lower of intertidal (S. alterniflora peat) 

 which had grown out over the accumulating sand. This suggestion requires more 

 detailed examination. 



It is certain that large areas of high marsh have been removed from its 

 margin and that this process is still going on. It would be most interesting to 

 understand what changes in the controlling influences have produced this rever- 

 sal in the process of marsh development. 



References 



Marmer, H. A. 1948. Is the Atlantic Coast Sinking? The Evidence from the 

 Tide. Geog. Rev. Vol. 38, pp. 652-657. 



Mudge, B. F. 1858. The Salt Marsh Formations of Lynn. Proc. Essex Inst. 

 Vol. 2, pp. 117-119. 



39 



