THE GEOLOGIC WORK OF MANGROVES IN SOUTHERN 



FLORIDA 



By T. WAYLAND VAUGHAN 



Custodian op MadrEporarian Corals, United States National Museum; 

 Supervising Geologist, in Charge oe Coastal Plain Investiga- 

 tions, United States Geological Survey 



With Seven Plates 



The importance of mangroves in building shallow submarine banks 

 into land and increasing the area of land of very low relief has been 

 observed and described in more or less detail by several geologists 

 who have studied the Florida coast and keys and the West Indian 

 islands. Professor Louis Agassiz, in his report on the "Florida 

 Reefs," has given a charming account of the origin of the mangrove 

 islands; Mr. Alexander Agassiz has also written about them in 

 his "Three Cruises of the Blake" ; and Mr. Robert T. Hill has de- 

 scribed them in his "Geology and Physical Geography of Jamaica." 

 Although the activity of mangroves as geologic agents is well known, 

 no series of illustrations showing the development of the plants and 

 the successive stages in their formation of islands has, to my knowl- 

 edge, been published. While studying the geology of the Florida 

 keys and the corals of the reefs and flats of the region, under the 

 auspices of the Carnegie Institution of Washington, I have had an 

 opportunity to take a number of photographs, and they, with the 

 information obtained in connection with those investigations, form 

 the basis of these illustrations and notes. My thanks are due Dr. 

 Alfred G. Mayer, Director of the Marine Biological Laboratory of 

 the Carnegie Institution, for the privilege of visiting nearly all of 

 the Florida keys. 



Mangroves {Rhizophora mangle Linn.) are small trees or large 

 shrubs, from lo to 20 feet tall, limited in their distribution to tropical 

 or semi-tropical regions and confined to low lands, growing either in 

 the water or so near the water that the soil in which their roots are 

 imbedded is perpetually saturated. These conditions— a tropical or 

 semi-tropical climate and low land margining the sea or extensive 

 flats only slightly below the level of the ocean — are realized in south- 

 ern Florida, and mangroves are there abundant. They border the 

 rivers near the ocean, margin most of the higher keys, and form 



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