[Illustration: FIG. 73--Lines of growth in a sand spit: Tucker Beach, New Jersey, as photographed from a height of 10,000 feet, showing the growth southward by successive ridges, which probably began as sand bars, grew to be barriers by wave action, were heightened by wind-blown sand, and finally were added to the main body of the spit by the final filling of the enclosed lagoons. To the right (east) is the Atlantic Ocean, showing waves and surf near the light-colored beach sand. Farther to the left are the ridges of sand made dark-colored by vegetation, bordered by light-colored beach sand on Little Egg Inlet, which appears to the south and west. Scale, about 1:14,000.] of this picture, greatly reduced, is reproduced as Figure 22. Several characteristic shore and salt marsh features are illustrated by this series of photographs, and these are reproduced in separate figures together with illustrations of special features in other places. [Illustration: FIG. 74--An island developing toward the stage of being tied to the mainland by a double tombolo, or connecting bar: Napatree Point, as photographed from a height of about 10,000 feet, connected to the east by Napatree Beach with the mainland at Watch Hill, R. I., and approaching connection to the north with the mainland near Stonington, Conn. On the outer side of the tombolos underwater shoals and bars are seen dimly at the right (south, Block Island Sound side) and more clearly at the left (west, Fishers Island Sound), where the boat landing is situated at the edge of a submerged shelf. The surf appears as a thin white line, the beach sand as a narrow light-colored belt, and the higher land as dark-colored areas on which houses and other structures stand. Scale, about 1:24,000.] 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). [Illustration: 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.]