The main features illustrated in detail, all of which are continually liable to change, making the keeping of a map of the area at all up to date impossible by ordinary means, are as follows: coast of low-lying mainland (Fig. 60); mud or peat-covered beach (Fig. 59); sandy beach (Fig. 63); barrier beach (Fig. 67); beach cusps (Figs. 61 and 62); recurved spits or sand hooks (Fig. 70 and others); compound hook (Fig. 72); lines of growth in the development of hooks (Figs. 73); tombolos and tied islands (Figs. 60 and 74).
Fig. 75—Oblique view of the mouth of Powells Creek, Virginia, on the right bank of the lower Potomac River, 5 miles west of the Naval Proving Grounds at Indian Head, showing at the left the inner channel winding through the slightly submerged shoals and fading out toward the right where the channel crosses the submerged terrace of the Potomac.
Another experiment was made by the Coast and Geodetic Survey off the coast of Florida, where the water is clear, in an attempt to photograph “the small coral heads and pinnacle rocks” which may be disastrous to boats. The report states that the results were unsatisfactory and concludes that airplane pictures are useful in “aerial photo-topography” but not in
Fig. 76—Channels, shoals, and terraces in a drowned river valley: Roberts Creek, 9 miles southeast of Yorktown, Va., an estuary tributary to Chesapeake Bay. Under the water in the drowned valley is seen the channel, “braided” in some places, and extending out through sand bars to the deep water of Poquoson River shown at the top (north) of the illustration. At the left the dark-colored forest area is fringed with a narrow strip of white beach sand, then with a belt of shallow water at the outer edge of which the waves form an irregular white line, and beyond this with a belt which represents a submerged terrace. Scale, about 1:14,000.