Island Sound to Carolina, such as the Delaware, Chesapeake, (Fig. 297) and numerous smaller bays, are the results of recent sinking, which has allowed the sea to invade the lower ends of river valleys. The ragged coast of Maine is another example, though glaciation as well as subsidence has been operative here. From the present configuration of coast-lines, it has been inferred that the present is, on the whole, an era of continental depression.[145] River valleys, the lower ends of which are embayed, are sometimes found to be continuous with submerged valleys beyond the coast-line (Fig. 298). Submerged river valleys show that the surface in which they lie was once land. [Illustration: +Fig.+ 297.—Sketch of the eastern coast of the United States from Cape May to Cape Henry, showing coastal irregularities. The figures represent the depths of water in fathoms. (From charts of C. and G. Surv.)] [Illustration: +Fig.+ 298.—Sketch of Carmel Bay, Cal. The contours below sea-level show a deep submerged channel. (From charts of C. and G. Surv.)] Bays may be developed by local subsidence as well as by the submerging of valleys, though decisive examples are not readily cited. Bays may also be produced by uplift of the surface on either side of an area which does not change its level. For example, uplift on either side of the Gulf of California has probably been one element, though probably not the only one, in the development of this indentation. The general outline of a great bay produced by coastal warping might be regular, though it would be likely to be marked by small irregularities where the streams enter. It is not to be understood that all, or even most, bays are due to local diastrophism. Diastrophism, then, as it affects the ocean-bottoms and the ocean-borders, may make the water of any ocean shallower or deeper; it may cause the emergence or submergence of land; it may make coast-lines regular or irregular; it may shift the habitat of life, and through these changes may greatly influence the processes of gradation, which are especially active along the contact of sea and land. =Vulcanism= affects the sea-bottom much as it affects the land. At the volcanic centers, where the great body of extruded matter accumulates, mounds and mountains are built up. Most of the mountain peaks of the sea-bottom, whether their crests are islands, or whether they are wholly submerged, have had a volcanic origin. The rock material ejected from submarine vents is probably less widely distributed than that from vents on land, and so far forth, the volcanic cones in the oceans are steeper than those on land. Where volcanic cones are built up near the surface of the sea, they often furnish a home for shallow-water life, such as polyps. Wherever built up so as to be within the reach of waves, gradational processes are stimulated.