MARINE MARSHES 



491 



mass, while at the same time the waves may cut back the beach 

 hne. Thus it may happen that a section of a marsh is exposed 

 along the shore, below the cover of dune sand. Examples of such 

 old marshes showing on the coast may be seen at Cape Cod, near 

 the Nausett Lights, on the coast of Nantucket, along the western 

 coast of Long Island (near Bath Beach), and elsewhere. 



The sequence of events thus outlined would lead to the forma- 

 tion of the following succession of deposits (Davis, C. A.- 

 1^^:626-/): At the bottom the section should show sand, silt, or 

 mud up to about twelve feet below low-water mark ; between this 

 level and that of low water should occur silt surrounding the easily 

 recognizable remains of the eel grass and mingled with it should 



Fig. iioa. Map of the Plum Island (Massachusetts) marshes, dissected by 

 meandering tidal streams. (After Shaler.) 



be the shells of molluscs and the remains of other marine organisms. 

 Above this should occur another layer of silty mud up to the level 

 above which the salt water grasses grow. The next higher stratum 

 should contain the remains of these plants in constantly increasing 

 numbers, until they form the bulk of the stratum. This would 

 result from the observed fact that there is a level above the low-tide 

 mark below which these plants do not go, while, at the greatest 

 depth at which they do grow, the number of individuals is small 

 compared with that found higher up. where these grasses find their 

 most favorable conditions for growth. "At the top of the section 

 should be a distinct turf, formed of the characteristic plants grow- 

 ing on the surface, which, because of the very definite fixed habits 

 of these species, would be, relatively, very thin." (Davis-15.) 



