672 DYNAMICAL GEOLOGY. 



Hippie-marks are often made by the waves over the finer beach- 

 sands, where they are low and partly sheltered, and also over mud- 

 flats. The flowing water pushes up the sand into a ridgelet, as high 

 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. Ripple-marks may be made, by the vibration of waves, even 

 at depths of 300 to 500 feet. 



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, flow- 

 ing by any half-buried shell or stone, may make rills in the sand, or 

 rill-marks (Fig. 63, p. 83). 



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

 beach-cleposits. Below high-tide level, there may be the vertical bor- 

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

 nassa family), and of 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 progressing Submergence or Emergence. 



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. What- 

 ever 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 preexisting 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 submergence, the 

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

 successively pass through the conditions of a seashore. On existing 

 seashores, the action in progress, instead of tending to excavate val- 

 leys, produces just the contrary effect. It is everywhere wearing off 

 exposed headlands, and filling up bays. The salt waters, in fact, enter 



