482 HARSHBERGER— THE ORIGIN AND 



ditions begin to prevail, that is along the inner tension line of the 

 salt marshes, we find Hibiscus moscheutos, Baccharis halimifolia 

 and Iva frutescens along with Ptilimnium capillaceum, Cicuta 

 niaculata, Myrica carolinensis and other plants, either in front of, 

 or in the center of the thicket vegetation. 



The surface conditions, which we have described above, may be 

 disturbed by the action of strong eddying currents of wind, which 

 blow across the salt marsh. The grasses and other marsh species 

 are blown down and become matted and twisted, so that marsh 

 surface has a billowy apearance (Plate X., Fig. 2) with extensive 

 areas of erect marsh plants, and depressed portions of greater or 

 less size of prostrated grasses. With exceptionally high tides, which 

 carry the dead stems, leaves, and other remains of the marsh plants 

 about with them, the floating material is carried in over the marsh 

 and deposited upon the surface of the salt marsh plants, especially 

 in the hollows of the grassy surface, which have been caused by the 

 wind (Plate X., Fig. 2, and Plate XL, Fig. i). These rafts of 

 vegetable debris are left on the surface of the marsh with the tidal 

 ;retreat, and as the water level may not rise again to a similar level 

 ior several days, or even months, the drift material smothers the 

 growing plants beneath it, and rapid decay sets in. This smothering 

 action may be effective in larger or smaller areas of the marsh 

 (Plate XL, Fig. i), and the tops of the plants are not only destroyed, 

 but the decay reaches the underground parts as well. Not only are 

 the underground parts destroyed, but also the surface of the salt 

 marsh sod, which is above the permanent ground water level. De- 

 pressions in the salt marsh are thus formed, which vary in size 

 from a few feet across to areas an acre or more in extent. These 

 depressions usually have steep sides and become filled with water at 

 high tides, and thus constitute the typic salt marsh pools (Plate XL, 

 Fig. 2 ; Plate XIL, Fig. i ) which are in evidence in every salt marsh 

 along the Atlantic coast. 



Various algae begin to grow in these quiet pools (Plate XL, 

 Fig. 2), and an investigation of the algae found in such pools at 

 Cold Spring Harbor, Long Island, showed the presence of the 

 following blue green algae: Lynghya scmiplena, Microcoleus chtoiia- 

 plastcs, Oscillatoria limosa, Rivularia atra and such diatoms as 



