WAVE-EROSION 



181 



and roofs of most sea-caves have a pronounced inclination land-- 

 ward, and if the cliff is low, the cave may be extended landward 

 until its roof is pierced. Through such an opening in the top of 

 the cliff the water of the incoming waves may be forced in the form 

 of spray. On the New England coast, such holes are sometimes 

 known as "spouting horns." Similar openings may be made by 

 the compression or rarefaction of the air in the cave as the wave 

 enters or retreats. Sea caves, "spouting horns," "pulpit-rocks," 

 and other isolated islets, all are closely associated with the sea-cliff 

 in origin. 



The bottom of the sea-cliff is bordered by a submerged platform 

 over which the water is shallow. This platform, or at any rate its 



1 86. Wave-cut terrace. The land has risen or the sea sunk since the 

 U-rnuv was cut. Seward Peninsula, Alaska. (U. S. Geol. Surv.) 



landward portion, represents the area over which the water has 

 advanced as the result of wave-cutting, and is known as the -wave- 

 cut terrace. Such a terrace is the necessary accompaniment of the 

 cliff. Wave-cut terraces may become land by elevation, or by the 

 lowering of the level of the sea (Fig. 186). Elevated sea-cliffs with 

 wave-cut terraces at their bases are among the best evidences of 

 change of relative level between water and land. 



Wave-erosion and horizontal configuration. The structure of 

 the rock along shore has much to do with the horizontal configura- 

 tion of the wave-shaped coast. Wave erosion develops re-entrants 

 in the weaker portions of the shore, leaving the more resistant parts 

 as headlands (Fig. 2, PI. VI. p. 69). It is to be noted that the resist- 

 ance of rock to wave-erosion is not determined by its hardness alone. 



