coastlines, active coral reefs are restricted to southern Florida, Hawaii, 

 Virgin Islands and Puerto Rico. On Some of the Florida coast, reeflike 

 structures are produced by sabellariid worms. (Kirtley, 1971.) Organic 

 reefs stabilize the shoreline and sometimes affect navigation. 



4.25 OCCURRENCE OF LITTORAL MATERIALS ON U.S. COASTS 



Littoral materials on U.S. coasts vary from consolidated rock to 

 clays, but sand with median diameters between 0.1 and 1.0 millimeters 

 (3.3 and phi) is most abundant. General information on littoral mate- 

 rials is in the reports of the U.S. Army Corps of Engineers' National 

 Shoreline Study; information on certain specific geological studies is 

 available in Shepard and Wanless (1971); and information on specific 

 engineering projects is published in Congressional documents and is 

 available in reports of the Corps of Engineers. 



4.251 Atlantic Coast . The New England coast is generally characterized 

 by rock headlands separating short beaches of sand or gravel. Exceptions 

 to this dominant condition are the sandy beaches in northeastern Massachu- 

 setts, and along Cape Cod, Martha's Vineyard, and Nantucket. 



From the eastern tip of Long Island, New York, to the southern tip 

 of Florida, the littoral materials are characteristically sand with median 

 diameters in the range of 0.2 to 0.6 millimeter (2.3 to 0.7 phi). This 

 material is mainly quartz sand. In Florida, the percentage of calcium 

 carbonate in the sand tends to increase going south until, south of the 

 Palm Beach area, the sand becomes predominantly calcium carbonate. Size 

 distributions for the Atlantic coast, compiled from a number of sources, 

 are shown in Figure 4-9. (Bash, 1972.) Fine sediments and organic sedi- 

 ments are common minor constituents of the littoral materials on these 

 coasts, especially in South Carolina and Georgia. Beach rock and coquina 

 are common at shallow depths along the Atlantic coast of Florida. 



4.252 Gulf Coast . The Gulf of Mexico coasts of Florida, Alabama, and 

 Mississippi are characterized by fine white sand beaches and by stretches 

 of swamp. The swampy stretches are mainly in Florida, extending from 

 Cape Sable to Cape Romano, and from Tarpon Springs to the Ochlockonee 

 River. (Shepard and Wanless, 1971, p. 163.) 



The Louisiana coast is dominated by the influence of the Mississippi 

 River which has deposited large amounts of fine sediment around the delta 

 from which wave action has winnowed small quantities of sand. Tul" oC-q 

 has been deposited along barrier beaches offshore of a deeply indented 

 marshy coast. West of the delta is a 75-mile stretch of shelly sand 

 beaches and beach ridges. 



The Texas coast is a continuation of the Louisiana coastal plain ex- 

 tending about 80 miles to Galveston Bay; from there a series of long, wide 

 barrier islands extends to the Mexican border. Littoral materials in this 

 area are dominantly fine sand, with median diameters between 0.1 and 0.2 

 millimeter (3.3 and 2.3 phi). 



4-22 



