THE OCEAN. 665 



as the force can make, and then plunges over the little elevation and 

 begins another ; and thus the succession is produced. The height 

 and breadth of the intervening space will depend on the force and 

 velocity of the flowing water, and the ease with which the sand or 

 mud is moved. Eipple-marks may be made by the vibration of 

 waves even at depths of 300 to 500 feet. 



The rapid in-flowing tidal or other current over the sands of sand- 

 bars, and the bottoms of bays, may produce an effect similar in 

 general character to ripples, although on too large a scale to be re- 

 cognized as such. The oblique lamination of layers, represented in fig. 

 61 e, p. 93, is probably a result in this way of a pushing action in 

 waves or currents. 



When a wave dies out on a beach, it sometimes leaves a tracing 

 of its sweep on the sand, as a wave-line ; and the returning waters 

 flowing by any half-buried shell or stone may make rills in the 

 sand, or rill-marks (fig. 63, p. 94). 



Broken shells, and other marine relics in fragments, are common 

 in beach-deposits. Below high-tide level, there may be the vertical 

 borings of sea-worms, of certain Crustaceans (as species of the Callia- 

 nassa family), and some Mollusks. In the off-shore shallow waters 

 occur beds of living Mollusks, and other kinds of animals, as well as 

 plants, varying according to the depth. 



4. Action of the oceanic waters over a submerged Continent, and during a gra- 

 dual submergence or elevation. 



1. Marine deposits. — The most obvious effect of the slow submer- 

 gence of a continent beneath the waters of the ocean would be the 

 working-over, by the waves and marine currents, of the loose earth, 

 gravel, and alluvium of the surface, thereby changing them into 

 marine deposits. The depth to which this alteration would extend 

 would, for the most part, be much less, probably, than a hundred 

 feet. Whatever the extent, the ocean, besides exterminating living 

 species, would obliterate most of the remains of terrestrial life in 

 the altered deposits, and introduce its own living Mollusks and 

 other tribes throughout the new continental seas. 



2. Features of the surface not altered by an excavation of valleys, but by a 

 diminution of its heights and a filling of pre-existing valleys. 



It might be supposed, at first thought, that the ocean would wash 

 through the valleys with great excavating force, and make deep 

 gorges over the surface. The real effect will be best learned from 

 the present action on sea-coasts; for with every foot of submer- 

 gence the sea-beach would be set a little farther inland, so that 

 the whole would successively pass through the conditions of a sea- 



