EFFECT OF FKLGRASS 233 



the currents of the tides which s\v(-ep throu^jh their inter- 

 stices. 



When the tide is high, tlie tops of the eelgrass plants are 

 some feet below the surface. Dm in;^- the period when there is 

 little motion to the water the sediment whicli ma\- have been 

 broLicrht up into it during the time when it was moving swiftly 

 settles between the st ems of the plan ts aad-liradual]\'_a£cumu- 

 lates at their base w^he re it is protected fromJ"urther disturbance. 

 Many species jof animals ^Iwell ami d the close-set he rbao^e^ find- 

 ino- inthose-jcaftditiaas--a-_jl ieasure of protection and a^ good 

 share of food. The remains of these creatures are also con- 



i!lllfs:r- 



!,;^,, 



b:KiiiliilllilllMi!liliiMl!llllllllllilllilllili!B^ :: :.'SiC:.:K.».J^ : , , i:;, :.:,;„„v , , i!,:i. ,:,:„:::;|!.|:„ ■ , I , li I, „ , „ 



Diagrammatic Section through a Growing Marino Marsh 



tributed to the grrowinor mass of detritus. In time these accu- 



o o _______ 



mulations rise to near the level of low tide. In this position 

 the eelgrass will no longer flourish, and for a time the deposit 

 of mud is apt to be left as uncovered ooze, or at most it bears 

 an imperfect coating of alga-. At this elevation, however, the 

 detrital matter is protected from the action of the swifter flow- 

 ino; tidal streams, for these move with considerable energy only 

 in the deeper water channels. The facts observable along our 

 northern harbors clearly show that the eelgrass does an exten- 

 sive work in diminishing the depth of water over large portions 

 of the harbor floors. 



While the eelgrass serves to shallow the water of our har- 

 bors to near high-tide mark, a number of plants are at work 

 in a different manner around the margins of these water areas. 



