So far as concerns the vertical configuration of coasts, erosion and deposition are in contrast, for while the former tends to develop steep, irregular, and often high slopes (p. 349) from the land to the sea, the latter tends to develop gentle, regular, and low ones. A partial exception to the latter part of this general statement comes about through the building of dunes, the material for which is furnished by the waves. SUMMARY OF COASTAL IRREGULARITIES. The horizontal irregularities of coasts are both large and small. Some of them, like Florida, Sandy Hook, etc., consist primarily of projections of land into the sea; others, like Chesapeake Bay, the Gulf of Mexico, and Puget Sound, are projections of the sea into the land; while still others, like the Gulf of California and its associated peninsula, cannot readily be put in either of the foregoing classes. Some of the irregularities of the land border, such as Yucatan, are more or less nearly normal to the general trend of the coast which they affect, while others, such as the “beaches” along the Atlantic and Gulf coasts of the United States (Figs. 319 and 320), are more or less nearly parallel with it. Some of the irregularities, especially some of the small ones, are more or less angular in their outline (Pl. XX and parts of Fig. 2, Pl. XXII), while others are bounded by curves instead. In many cases more than one factor has been involved in the development of irregularities. In the case of great irregularities, diastrophism has generally been the dominant factor. The Gulf of Mexico and the Mediterranean Sea perhaps represent differential subsidence, while Florida and the Iberian peninsula represent differential uplift (relative, though perhaps not absolute). The narrow bays which indent many coasts generally represent the subsidence of a region previously affected by valleys (Fig. 297). Many of them, such as Narragansett, Delaware, and Chesapeake Bays, are primarily the drowned ends of river valleys, while others, such as Puget Sound,[167] are primarily structural valleys (synclines). Many of the long and narrow bays or fiords common in the high latitudes of North America and Europe (Fig. 266, p. 293) appear to be the drowned ends of valleys previously deepened by glaciers. The drowned ends of river canyons, and the submerged parts of valleys excavated (not sunk) beneath the sea by glaciers, would also be fiords. [Illustration: PLATE XXIII. Fig. 1. MASSACHUSETTS. U. S. Geol. Surv. Fig. 2. MAINE. U. S. Geol. Surv.] [Illustration: PLATE XXIV. PORTION OF THE COAST OF MAINE. U. S. Geol. Surv.]