VI. DEVELOPMENT OF A BARRIER ISLAND 



The findings of this study give all major barrier-island theories some 

 support. As early as Dana (1894) and Gilbert (1890) littoral transport 

 was considered a valid barrier-building mechanism. Johnson (1925) suggested 

 that wave-cut drumlins provided sediment for the development of spits and 

 pocket beaches in the Nantasket area near Boston, Massachusetts. Figure 

 34 is a reproduction of a similar suggestion by Nichols (1941) for the 

 development of Castle Neck. Nichols did not have the benefit of subsur- 

 face data, and was unaware of the Pleistocene topography of the south- 

 eastern end of Castle Neck. 



Hoyt (1967) proposed relict beach ridges as the origin of barrier 

 islands. Fisher (1968) suggested a mechanism similar to that of Gilbert's 

 (1890) spit-accretion. There are in this study area drowned relict drum- 

 lins linked by deposits caused by littoral drift. However, the erosion 

 of the drumlins was not the only source, because the Merrimack River was 

 contributing large amounts of sediment during the building of the barrier 

 islands and spits. 



The remainder of Plum Island (north of Camp Sea Haven, Figures 1 and 

 2) which was not part of this study area, may have a structure similar to 

 the southern end of the island. It is suggested that Pleistocene topography 

 and bedrock highs anchor the island at these locations. Anan (1971) finds 

 evidence in his offshore sediment analysis of a relict delta near the mouth 

 of the modern Merrimack River. The delta was flanked by low barriers which 

 probably moved landward in response to the sea's transgression. A three- 

 dimensional analysis of other barriers on this coast would certainly ex- 

 pand the historical and stratigraphic concepts of the Pleistocene and Holo- 

 cene sediments. 



55 



