The presence of a soil zone under a portion of the large barrier chain, which makes up much of the North Carolina coast, and the absence of this zone under the remainder of the barrier has led to a re-evaluation of the mode of formation and the evolutionary development of this stretch of coastline during Holocene time.
A primary barrier, formed during a rising sea, became detached by flooding of the area behind a mainland beach. This primary barrier apparently reoccupied the position of a barrier formed during a stillstand within the general Wisconsin regression.
The present coastline has evolved from the primary barrier by retreat and migration of headlands as well as formation of secondary barriers, by spit elongation, over the adjacent continental shelf. Approximately 61 percent of the present barrier chain is secondary in nature; whereas the remaining 39 percent is modified primary.
Continued retrogression of the barrier islands eventually will superimpose the secondary barriers over the primary. When this happens, evidence that a secondary barrier existed will be obliterated. The extreme case results when this compound barrier is driven landward until it eventually reaches the mainland, hence a mainland beach. At this time, no evidence remains that any barrier previously existed. The presence of a secondary barrier would suggest the landward presence of a primary barrier or a mainland beach.