=Coast terraces.=—Upon those shores where to-day high mountains front the sea, the coast may generally be seen to rise in a series of terraces (Fig. 278). This is notably true of those coasts which are to-day racked by earthquakes, such as is the eastern margin of the Pacific from Alaska to Patagonia. The traveler by steamer along the coast from San Francisco to Chili has for weeks almost constantly in sight these giant steps on which the mountains have been uplifted from the sea. In Alaska we are fortunate in having the history of the later stages in this uplift (Fig. 279). As described in a former chapter, portions of this shore rose in the month of September of the year 1899 in some places as high as forty-seven feet, to the accompaniment of a terrific earthquake and sea wave. Above the terrace which marks the beach line of 1899 there is a higher terrace of similar form now overgrown with trees, but none the less clearly to be recognized as a shore line of the past century which preceded in the long sequence the uplift of 1899. [Illustration: FIG. 279.—Uplifted sea cliffs and terraces on the coast of Russell Fjord, Alaska (after Tarr and Martin).] [Illustration: FIG. 280.—Diagrams to show how excessive sinking upon the sea floor will cause the shore to migrate landward as it is uplifted.] [Illustration: FIG. 281.—A drowned river mouth, or estuary upon a coastal plain.] As was noted in our study of earthquakes, the recent instrumental records of distant earthquakes tell us that the movements upon the sea floor are many times larger than those upon the continents, and that while the mountainous coasts are generally rising, the deeps of the sea are sinking. The effect of this over-balance of sinking, or resultant shrinking of the earth’s shell, may be to compress the mountain district and so cause the shore line to move landward at the same time that it moves upward (Fig. 280). =The sunk or embayed coast.=—When now, upon the other hand, a section of the coast line sinks with reference to the sea, the water invades all the near-shore valleys, thus “drowning” them and yielding the drowned river mouth or _estuary_. If the relief of the shore was slight, as it generally is upon a coastal plain, slight depression only will produce broad estuaries, such as Chesapeake Bay at the drowned mouth of the Susquehanna (Fig. 281). If, on the other hand, the relief of the shore is strong and the subsidence is large, the entire coast line will be transformed into an archipelago of steep-walled rocky islets which rise abruptly from the sea (Figs. 282 and 284). A plateau which is intersected by deep and steep-walled valleys of U-section (p. 341) under large submergence yields the _fjords_ so characteristic of Scandinavia or Alaska. A ragged coast line, fringed with islands as a result of submergence, is described as an _embayed coast_. [Illustration: