HUMID AREAS AND THEIR RECLAMATION 61 



All these marsh soils have been formed under excessive 

 moisture conditions. Their formation, classification, and 

 characteristics are very interesting. 1 Their agricultural 

 value depends finally upon the removal of the excess of 

 water and upon their later management. 



87. Marine marshes. These marshes have been pro- 

 duced by the filling of arms of the sea by dense growths 

 of marine vegetation. To this mass have been added con- 

 siderable amounts of silt and the shells and skeletons of 

 marine life by the action of the tides. Many of these 

 marshes are very rich and when reclaimed prove very 

 productive. Shaler places the area of the marine marshes 

 of the United States, " including only the deposits which 

 are bared at half tide, and which owe their formation 

 mainly to the growth of grass-like plants," at nearly 10,000 

 square miles, over 6,000,000 acres. 2 



88. Reclamation of common swamp lands. The adap- 

 tation of these over-wet areas for agriculture has brought 

 forth numerous and extensive reclamation projects. For 

 many years the drainage of large areas of flat prairies, by 

 extensive open ditch or canal systems, has been in progress 

 in Illinois, Iowa, and other prairie states. One such area 

 in Illinois is known as Vermilion River District. Its 

 main ditch is 10 miles in length, 70 feet wide at bottom 

 and 9 feet deep. In most cases the great main ditches of 

 these prairie drainage enterprises find an outlet by gravity 

 into some natural waterway, such as a stream or river, 

 as is the case with the Vermilion District. In some cases, 

 however, dikes must be built, and pumping stations pro- 

 vided to lift the water out. 



1 See Davis on Peat. State Dept. of Geology, Mich. 



2 12th Annual Report Director U. S. Geological Survey, p. 

 319. 



