[Illustration: FIG. 30 (left)--Sand bars and drowned terrace about Stove Point Neck, at the mouth of the Piankatank River, Virginia, as photographed from a height of about 10,000 feet at 11:30 A.M., December 11, 1920. West (left) of the neck, at the outer edge of the terrace, the water is 2 to 3 feet deep at low tide, or 5.7 feet and 6.7 feet at high tide, but deepens abruptly westward, where it is 20 to 30 feet deep in Fishing Bay (see Fig. 32). To the south and east of the point the abrupt descent is at the side of the deep channel of the Piankatank River. To the right, the bottom, having a wavy appearance because of sand bars, fades off more gradually under deep water. The mottled area in the middle of the neck is wooded, and the smoother parts near the point and in the upper part of the neck are cleared land. Scale, about 1:30,000.] [Illustration: FIG. 31 (right)--Drowned terraces at Gwynn Island at the mouth of the Piankatank River, Virginia, as photographed from a height of about 10,000 feet at 11:30 A.M., December 11, 1920. At the right is a part of the island, showing trees, fields, and houses. Bordering the land area is a narrow band of light-colored beach sand, expanded at Cherry Point into a conspicuous sharply recurved hook. Under the shallow water can be seen wave marks resembling large ripple marks. The water is 2 to 3 feet deep at low tide at the outer edge of the light-colored submerged shelf, beyond which the bottom descends abruptly toward the left to a depth of about 20 feet. North of Cherry Point the waxy bottom shades off more gradually to the deep channel of the Piankatank. Scale, about 1:30,000.] THE BEST CONDITIONS FOR PHOTOGRAPHING UNDERWATER LAND FORMS [Illustration: FIG. 32--Part of the Kilmarnock and Mathews, Va., topographic sheets, 1:62,500, published by the U. S. Geological Survey, showing the location of Figs. 31 and 32; and a cross section along the line indicated on the map, showing a terrace 26 feet above sea level at the left, one less than 5 feet above water level on Gwynn Island, one 5 feet or less below water level; and the river channel with abrupt banks between the shoals. Scale, 1:70,000.] The photographic study of underwater land forms is relatively new, and little information concerning it is available. It is annoyingly obvious to the air observer that at times he can see nothing beneath the surface of the water, whereas at other