482 THE JOURNAL OF GEOLOGY. 



to the shore, whatever force the waves may have is expended 

 at the water's edge. On a bold coast they carve sea-cliffs 

 and grind shingle with sand. Such are the coasts of 

 New England, Oregon, California, and of all the Pacific 

 side of South America. The resulting sediments are com- 

 posed of worn but fresh rock fragments and thus bear witness to 

 rapid mechanical erosion, like the products of rock breaking on 

 steep declivities. On a shore of incoherent materials waves stir, 

 wash and separate fine and coarse, light and heavy particles. 

 Under favorable conditions of depth of water and long fetch, 

 waves thus sort a heterogeneous mass of gravel or of residual 

 sand and clay more efficiently than any other agent, and leave 

 clean cross-stratified beach sand and gravel with boulders, while 

 the finer materials are swept away. The southeastern shore 

 of Long Island presents a conspicuous example of this, and 

 the westward drift of the beach-sands is illustrated in the fact 

 that shingle beaches prevail toward the eastern end of Montauk 

 point, and the sands there washed from the bluffs of glacial 

 gravel form long barriers along the coast to the westward. 



If, on the other hand, waves break in shallow waters at a dis- 

 tance from shore they there build a barrier, and the height to 

 which they build it above high tide is the measure of their max- 

 imum power during great storms. Within the barrier then ex- 

 tends a lagoon. The whole Atlantic coast from Long Island to 

 Florida is thus fringed by the features of prevalent wave action, 

 due to the great fetch from off the ocean and the gradual slope 

 of the continental platform. 



(£) Prolonged transportation. — Sorting is also accomplished 

 to some extent, though less perfectly, by deep water and con- 

 tinuous currents. Sediments settle unequally according to size 

 and specific gravity of particles; therefore the largest and heav- 

 iest reach bottom first, the finer and lighter later, and the finest 

 and lightest last. If the conditions of supply or current be in- 

 termittent over any area then each incident of deposition will be 

 marked by a layer composed of coarsest grains below and finest 

 grains on top. This is the nature of deposition in tidal estua- 



