TUlilR VALUE FOR TJLLAGK 



239 



ever, a dike was constructed which debarred the tide from the 

 area it had visited the haven was rapidly shoaled by the incur- 

 sion of sands and became almost worthless for the shelter of 

 such craft as had previously resorted to it. On this account it 

 will be necessary carefull\' to consider the effect of all opera- 

 tions looking to the reclamation of tidal marshes. 



Dike and Marshes, Green Harbor River, Marshfield. Massachusetts 



It is a very general fact that in hiq;h latitudes, usually in all 

 districts to the north and south of the tropical realm, vegetation 

 of the marine marshes consists altogether of plants which have 

 only annual tops, though their roots may endure for years. No 

 bushes or trees will grow on these marshes so long as they are 

 visited by the tide. In the warmer districts, within or near the 

 tropics, we find certain species of trees which have become 

 reconciled to the peculiar conditions imposed by havmg their 



