352 Annals of the Carnegie Museum. 



' Stage B. — Lagoons C and G. 



(a) The Potamogeton formation, 



((^) T\\e. Juncus-Eleocharis formation, 



(^) The Populus-Salix formation. 



Around Lagoons C and G (see map) the Potamogeton and Populus- 

 Salix formations are older and somewhat more mature than around 

 Lagoon Aa, although otherwise essentially the same. Inside the Pop- 

 ulus-Salix zone, however, there is a new zone, which from its facies 

 may be termed the Juticus-Eleocharis formation (see Plate XLI). 

 This formation is also to be seen at the extreme northern end of 

 Lagoon Aa, where encroachment of the sand upon the water is pro- 

 ceeding more rapidly. 



T\ie /uncus- Eleocharis Formation. 



The hedge of small cottonwoods and willows constituting the Pop- 

 ulus-Salix formation serves as a partial protection against the drifting 

 sand and the habitat {edaphic) of the inner zone is thus formed of a 

 more compact soil of a finer texture, which is not easily worked over 

 by the little waves of the lagoon, and thus does not afford suitable 

 conditions for the burial and ecesis oi Populus or Salix. However, 

 the zone is soon occupied by a formation of rush-like and sedge-like 

 plants, mostly spreading about in the wet sand by means of rhizomes. 



The structure of the formation is : 



Facies. — 



/uncus balticus littoralis, Eleocharis acuminatus, 



Eleocha7'is obtusa. 



Prijicipal Species. — 



Tfiglochin palustris, Carex Oederi puniila. 



Secofidary Species. — 



Cypenis flavescens. 



Each of the two species of Eleocharis, by aggregation, usually form 

 closed circular mats (families and communities), into which no other 

 species of the local flora appears able to penetrate and which often 

 accumulate the sand quite rapidly, appearing then in miniature dunes 

 two or three inches above the surrounding sand, these patches increas- 

 ing in area radially by the further growth of the rhizomes of the Eleo- 

 charis (see Plate XLII). 



