-8- 



and Cameron, 1976). Rise in sea level caused the salt water 

 to inundate the freshwater marshes along the mainland, 

 allowing salt marsh vegetation to encroach upon the 

 freshwater vegetation. This lead to the development of the 

 extensive salt marsh system present today behind the island. 

 Rapid sea level rise subsided in this area around 3,400 

 years ago (Mclntire and Morgan, 1964). Plum Island 

 continued to enlarge, however, eventually becoming attached 

 to the drumlins at the southern tip of the island (Rhodes, 

 1971) . Current sea level at Plum Island is approximately 

 the same as it was 2,000 years ago (Mclntire and Morgan, 

 1964) . The actual process by which the island formed is 

 still a matter of controversy. Mclntire and Morgan (1964) 

 concluded that transgressive sea level changes eroded and 

 reworked the glacial sediments, bringing about the formation 

 of Plum Island. Rhodes (1971), through seismic refraction 

 and wash bore sampling, obtained data that gave all major 

 barrier island theories some support. Jones (1977, p. 164) 

 studied the Plum Island-Castle Neck barrier beach system and 

 proposed a new mechanism for barrier island formation. He 

 concluded that "...the high storm energy transportation of 

 sand with spit development is a significant factor for the 

 development and migration of barrier island systems." 



From information obtained through peat cores 

 (McCormick, 1969; Mclntire and Morgan, 1964), wash bore 

 sampling and seismic refraction, (Rhodes, 1971), an early 

 picture of this area can be developed. Some 6,000 years ago 

 the island was a developing sand spit with the drumlins (Bar 

 Head, Stage Island, Grape Island, and Cross Farm Hill) 

 forming upland islands to the south. A fresh water marsh 

 fringed the mainland along with an encroaching salt marsh. 

 Along the west edge of this developing sand spit there 

 probably existed a small fringe of salt marsh. The area 

 between the spit and the mainland was mostly open water. As 

 time progressed, sea level rose and the sand spit continued 

 to enlarge and migrate westward over the developing marsh. 

 The marshes themselves grew, closing the gap between the 

 mainland and the developing island. As sea level rise 

 slowed, around 3,400 years ago, the developing sand spit 

 became anchored to the drumlins at its southern end, forming 

 the Plum Island of today. 



Because of the dynamic nature of the dune system it is 

 impossible to predict exactly what the topography of the 

 island looked like during its early stages of development. 

 It seems reasonable to conclude that the foredune area 

 appeared much the same as it does today while the backdunes 

 were probably less stable and smaller than those now 

 present. 



