When dunes migrate into a timbered region they bury and kill the trees (Fig. 17). In one instance on the coast of Prussia a tall pine forest, covering hundreds of acres, was destroyed during the brief period between 1804 and 1827.[17] At some points in New Jersey orchards have been so far buried within the lifetime of their owners that only the tops of the highest trees are exposed. Trees and other objects once buried may be again discovered by farther migration of the sand (Figs. 18 and 19).[18] [Illustration: +Fig.+ 18.—A resurrected forest. The dune sand after burying and killing the timber has been shifted beyond it. Dune Park. Ind. (Meyers.)] Eolian sand, not aggregated into distinct dunes, is often destructive. Even valleys and cities are sometimes buried by it. Drifting sands had so completely buried Nineveh two centuries after its destruction that its site was unknown. =Distribution of dunes.=—Dunes are likely to be developed wherever dry sand is exposed to the wind. Their favorite situations are the dry and sandy shores of lakes and seas, sandy valleys, and arid sandy plains. Along coasts, dunes are likely to be extensively developed only where the prevailing winds are on shore. Thus about Lake Michigan, where the prevailing winds are from the west, dunes are abundant and large on the east shore, and but few and small on the west. In shallow water, shore currents and storm waves often build up a reef of sand a little above the normal level of the water. When the waves subside, the sand dries and the wind heaps it up into dunes. This sequence of events is in progress at many points on the Atlantic Coast. Sandy Hook, New Jersey, and the “beaches” farther south started as barrier ridges. When the waves had built them above normal water-level, the wind re-worked the sand, piling it up into mounds and hillocks (Fig. 1, Pl. II). Such dune belts a little off shore are sometimes turned to good account. They are usually separated from the mainland by a shallow lagoon. Where land is valuable, the lagoon is sometimes filled in, making new land, thus anticipating the result which nature would achieve more slowly. This has been done at some points on the western coast of Europe. [Illustration: +Fig.+ 19.—Migration of dune sand exposing bones in a cemetery. Hatteras Island, N. C. (Collier Cobb.)] Dunes are likely to occur along stream valleys (Fig. 2, Pl. II), if their bottoms or slopes are of sand, and not covered by vegetation. Dunes along valleys are usually on the side toward which the prevailing winds blow. Thus they are more common on the east side of the Mississippi than on the west. Dunes may be formed in the valley bottoms, but the sand is often blown up out of the valley and lodged on the bluffs above.