THE WORK OF THE OCEAN. 365 



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,^ 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. 

 The processes which develop coastal indentations, together with the 

 antecedent subaerial and the subsequent wave gradation, account for 

 most of the islands which affect indented coasts. Some of them are 

 high and some low for reasons which will be readily understood. The 

 long narrow belts of land constituting irregularities parallel to the gen- 

 eral trend of the coast (Figs. 319 and 320) are usually the result of depo- 

 sition in shallow water. They are usually sand or coral reefs, built 

 up above water-level by waves. The deposits at the debouchures of 

 streams give rise to projecting deltas. Most small irregularities of 

 angular form, especially if high (PL XX), indicate wave-erosion, and 

 their details of form are determined by the structure of the rock along 

 shore, while most irregularities of curved outhne involve something of 

 shore-deposition, if not due wholly to it. Glaciation, or glaciation and 

 subsidence, may also give rise to peninsulas, capes, and islands of 

 curved outhnes (PL XXIV, coast of Maine). Curving outlines may, 

 however, be developed by erosion alone in weak rock structures. This 

 is illustrated by the weak rock structures (clay, sand, etc.) of most of the 

 Atlantic coastal plain. Thus inspection of the horizontal configuration 

 of coasts will often indicate the processes which have been dominant 

 there in recent times. On the other hand, the interpretations of many 

 coastal irregularities, such as Hudson Bay, Puget Sound, the Gulf ot 

 Cahfornia, the Baltic Sea, etc., are not to be read from the map. In 

 such cases, diastrophism and gradation have usually cooperated, but 



1 Willis. Bull. Geol. Soc. Amer., Vol. IX, p. 113, and Tacoma, Wash., Folio, U. S. 

 Geol. Surv. 



