MARINE MARSHES 487 



The reed association or phragmitetum is not wholly restricted to 

 the low moors, but also occurs, though more sparingly, on the high 

 moors. The same may be said of certain sedge associations or 

 cyperacetes. Among the mosses certain species of Hypnum (as, for 

 example, H. fluitans, giganteum, and trifariuni, in Europe, and cer- 

 tain Sphagnums) occur with the reed associations, partly forming 

 floating mats or growing among the reeds. The sphagnums are 

 most characteristic of the high moors. 



The following classification comprises the important subdivi- 

 sions of the areas of deposition of modern caustobioliths : 



A. Marshes — Marine. 



1. Sapropelite region — submerged. 



a. Eel grass marsh. 



b. Mud flat region. 



2. Humulite region — emerged. 



a. Grass or Spartina marsh. 



b. Mangrove marsh. 



B. Szvamps — Fresh Water. 



1. Sapropelite region. 



2. Humulite region. 



a. Moss or Hypnetum zone. 



b. Sedge or Cyperacetum zone. 



c. Reed or Phragmitetum zone. 



d. Tree or arboretum zone. 



(i) Alder or Alnetum zone. 



(2) Cypress or Taxodetum zone. 



(3) Tupelo or Nyssetum zone. 



C. Bogs — Terrestrial. 



1. Forest moors. 



2. Upland bogs (High Moors). 



Marine Marshes. 



The development of marine marshes proceeds in the following 

 manner (Shaler-41 : 559; Davis, W. M.-16) : An off-shore sand 

 bar is built by the waves on the gently sloping sandy sea-bottom, 

 or a barrier beach is built between two projecting headlands. The 

 scouring action of the tides will keep open a channel through this 

 beach so that a connection between the sea and the lagoon is always 

 maintained. Bars may be built in water from 20 to 30 feet in depth, 

 and are due to the breaking of the large waves off shore, which 

 then pile up in front of them the detritus which they have dug up 



