ALONG SIIORE 
to the shore when the tide is out, and pile them 
over the tops of broken masts, sea-weed, and 
rubbish, until they make a bank that may be a 
barrier against the wave. Once a mound is 
made it is held in place by the hardy grasses 
and scrub-vegetation that grow on its sides 
and top. The mound or bank may keep add- 
ing to itself in this way until it stands a hun- 
dred feet high along the coast, and makes an al- 
most impregnable sea-wall. Behind such pro- 
tection as these sand-dunes, and by the building 
of dikes across the ocean inlets, thousands of 
acres of water have been turned into green 
pasture-lands and flat fields. Holland is an 
illustration of it. 
There is still another way by which the land 
gains upon the sea. The rivers, coming from 
a great distance inland, flood drift and dirt 
into the ocean. After a time the mouth of 
the river begins to choke up with muddy de- 
posits; a bar and then a bayou or lagoon is 
formed, a marsh begins to rise above the waters, 
seaweed accumulates, rushes and flags spring 
into life and make the ground stable; and 
after many years a group of islands, or perhaps 
a habitable meadow-land, is formed. Venice 
was builded upon such a formation, caused by 
Sea-bar- 
riers. 
Bars, la- 
goons, and 
marshes, 
