INTRODUCTION 
Salt marshes reach their best development where the coast nas long been 
slowly sinking. Their extent indicates the degree to which low-lying shores 
and the estuaries of streams are being "drowmed", It does not take a highly 
skilied engineer to make convincing observations as to the sinking of the 
Atlantic coast, Anyone seeing stumps of trees standing well out in salt water, 
in some cases 10 to 15 feet under low tide, ikmows that where they grew was once 
dry land, and that either the sea has risen or the land fallen, the latter seem- 
ing by far the more likely supposition. Such groups of stumps standing in nat- 
ural position, just as they would in a clearing, may be seen at numerous points 
along the Atlantic coast. Another evidence of sinking is the channels of streams 
which extend far seaward under water where they could not have been cut except 
when the vottom in that quarter was marsh. 
Engineers have measured the subsidence of the Atlantic coast and obtain- 
ed results indicating a sinking of about a foot in a hundred years. This seems 
no cause for’alarm, but if continued it may in time have serious consequences 
for many coastal cities. The case shows well, however, how Nature may work on 
a much larger scale than man. Man puts up great buildings at some of the lowest 
points on the coast, then marvels at his own works, while Nature in time may 
render them as naught through gradually and quietly letting down more than a 
thousand miles of coast line. : 
ZONES OF SALT MARSH PLANTS 
This sinking, as stated in the beginning, is a great aid to the forma- 
tion of extensive salt marshes. As the ocean slowly creeps up on the land salt 
water kills ordinary land plants. Their place is taken by others that can en- 
dure a slight. amount of salt in the.soil and live through occasional overflows 
of brackish water. Such plants occupy the inner beach zone, further details 
concerning which are given later. Just outside of this zone, where the soil is 
a little wetter and there are small channels and sometimes ponds, is the marsh- 
hay zone. Finally, where salt water stands continuously and there are large 
channels or guts, lakes, or lazoons, comes the tall cord or thatch grass. Such 
are the crief parts and plants of the Atlantic-coast salt marshes. The extent 
of these zones depends on the amount of tide. On the northern Massachusetts 
coast it is estimated that the vertical scope of the zones is: Beach, 1 foot; 
marsh hay, 2 feet; and cord grass, & feet. 
The zones of salt-marsh plants are not stationary, but rather may be 
regarded as ceaselessly shifting. To illustrate by a more familiar example, 
consider that in and about shallow fresh-water lakes similar zones of vegeta- 
tion may be seen, deperdent in this case chiefly on the water level in rela- 
tion to the scil in which plants are rooted. In many cases, as is well known, 
the lakes ere filling up. We see that the under-water plants help to anchor 
the muck and by catching silt and adding their own remains annually to the 
bottom mud, thicken and build it up, so that bulrushes and cattails can get a 
foothold. These increase and again, by filling the soil with roots and ac- 
cumilating more silt, harden the bottom and shallow the water another degree 
so that various sedges and grasses come in. They continue the process, en- 
abling alders, other bushes, and finally trees, to occupy a land area that 
once was water. 
