=Characteristics of shallow-water deposits.=—Clastic sediments laid down in shallow water have several distinctive characteristics. While they are, in the aggregate, coarse, they are characterized by frequent variations in coarseness. The surfaces of successive beds are likely to be ripple- and rill-marked (Figs. 324, 325, 326), and cross-bedding (Fig. 327) is of common occurrence. Clayey sediments accumulated between high and low water are often sun-cracked (Fig. 328), and the tracks of land animals are sometimes preserved on their surfaces. Shallow-water deposits often contain fossils of organisms which live in waters of slight depth. These characteristics are sufficient to differentiate sedimentary formations made in shallow water from those made in deep water, even after they have been converted into solid rock and after the rock has emerged from the sea. Many of these characteristics are, however, shared by deposits made by streams on the land. Subaërial and lacustrine sediments are usually distinguishable from those made in the sea by their fossils, and sometimes by their distribution. [Illustration: +Fig.+ 327.—Cross-bedding. (Gilbert.)] [Illustration: +Fig.+ 328.—Sun-cracks. These cracks were on the mud-flats of the Missouri a few miles above Kansas City, but the sun-cracks on shore-deposits are not essentially different. (Calvin.)] =Topography of shallow-water deposits.=—The shallow-water deposits have, on the whole, a rather plane surface, though there are some notable departures from flatness. The steep slopes of the delta fronts and of wave-built terraces have already been spoken of. Barriers often shut in depressions, and the disposition of the material deposited is sometimes uneven, owing to shore and tidal currents. The result is that the surface of the shallow-water deposits is often affected by low elevations and by shallow depressions. The elevations and depressions may be elongate, circular, or irregular in form. These general facts are shown in Figs. 319, 320, and 329. This topography is sometimes preserved on newly emerged lands, as at various points on the Coastal Plain of the United States. [Illustration: +Fig.+ 329.—Irregularities of topography of shallow-water deposits. The depths of the water are shown in fathoms. (Chart of C. and G. Surv.)]