THE WAVE 8 TOOTH 



153 



low sand barrier, is covered with shore grass, 

 and makes a protection for a bay or sound back 

 of it. 



Frequently the building of sea barriers is 

 helped by the deposit of streams. The rivers 

 are continually carrying down immense quan- 

 tities of silt and sediment. The bulk of this 

 silt is carried only a few miles from shore be- 

 fore it begins to settle to the bottom. The 

 result is soon apparent in a bar or lido, made 

 up of sand and river mud upon which vegeta- 

 tion grows and lends stability to the accumu- 

 lating soil. With the sea once shut out a la- 

 goon is formed reaching landward, and the 

 tendency is for this lagoon to grow long grasses, 

 gather vegetable and animal life to itself, and 

 form small islands. The islands are often 

 started by tangled bunches of sea weed, knit 

 together by growing grasses, and made into a 

 thick mat by various roots and weeds of the 

 water. Frequently they are spongy in charac- 

 ter and when walked upon bend like thin ice. 

 And they may also drift about from place to 

 place with the wind, lacking a foundation or 

 anchorage. Such an island, some years ago, 

 blew into the harbor of Dulutli on Lake Su- 

 perior during a storm, and was towed out by 

 tugs several days later. 



Sea har- 

 riers. 



Lapoons 

 and islands. 



