356 Annals of the Carnegie Museum. 



hedge-like appearance of the formation is disappearing, and the en- 

 vironment is becoming changed, because there is a much greater 

 illumination of the soil about the base of the trees. 



Stage D. — Lagoons C, D, and end of G (see Plate XLIV). 



(a) Potamogeton Formation, 



{b') Typha-Scirpus Formation, 



(^) Sabbaiia-Liimm Formation, 



{d') Myrica-Salix Formation, 



(^) Popiilus-Salix Formation. 



Stage D presents most of the formations in essentially the same con- 

 dition as they were described for Stage C, but in the more advanced 

 portions of the vegetation of the banks around the lagoons mentioned 

 in the heading there appears a new formation, so that it seems best to 

 indicate a stage of the succession coincident with the entrance of the 

 new formation, which may be called from its facies the Myrica-Salix 

 thicket-formation. 



The Myrica-Salix Thicket-formation. 



With the further advance of the sand upon the lagoon and the conse- 

 quent widening of the bank inside of the Populus-Salix zone, there is 

 a forward movement of the Sabbatia-Linum formation, at the same time 

 that its outer border is being invaded and taken over by the Myrica- 

 Salix formation, the latter thus forming a zone between the Sabbatia- 

 Linum formation and the Populus-Salix formation. 



The Myrica-Salix formation is a typical shrub association and is 

 characterized by the wax myrtle, Myrica carolinensis, and the two 

 willows, Salix discolor and Salix cordata. The ecotone between the 

 two willows of this formation and the Salix syrticola of the Populus- 

 Salix formation is very striking, but when the ecological conditions 

 obtaining in the two habitats at the time of ecesis of the respective for- 

 mations are considered, the apparent similarity of conditions is not so 

 great. The one willow accomplished ecesis under practically sand- 

 bar conditions, while the other two found suitable conditions in the 

 more compact, damp, humus-containing soil of the rosette zone {Sab- 

 batia-Linum formation). 



The structure of the Myrica-Salix formation is thus : 



Facies. — 



Myrica carolinensis, Salix cordata, 



