EFFECT OF SEA BARRIERS UPON DRAINAGE 449 
barrier of ‘‘alluvium”’ enclosing Barnegat Bay on the coast of 
New Jersey is from three to five miles from the contact between 
the ‘‘alluvium” and the older beds of gravel, sands, and clays. 
If Barnegat Bay were silted up by sediments from the landward 
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Fic. 4 is a further development of Fig. 3; the “lagoon portion” of the old stream 
having for the most part settled itself down in the underlying strata. The contact 
between the newer strata and the older being shifted seaward by erosion, the line of 
contact is some distance to the seaward from the stream. If the underlying older 
beds are very hard, the stream might continually shift itself along the line of contact, 
instead of cutting down into the hard beds below. A part of the old “lagoon portion,” 
instead of cutting down into the underlying rocks, is shown as having been shifted 
down the dip of the newer beds, and as flowing parallel with the contact but to the 
seaward of it. 
side, its lagoon might be shifted close up against the barrier. 
If, under these circumstances, this coast should be elevated and 
the shore line should be shifted some miles seaward, the ‘lagoon 
portion”’ of the resulting stream would be approximately parallel 
