320 PROCEEDINGS OP THE AMERICAN ACADEMY. 



the finer particles are moved seaward, beyond the limits of Figure 3, 

 where they are distributed in moderate thickness over a considerable 

 area. During this process, we may imagine the storm waves to say : 

 " We cannot to advantage attack a coast where the off-shore water 

 shoals so gradually ; let us therefore first deepen the off-shore bottom, 

 so that we may afterwards make better attack on the coast." So say- 

 ing, a preliminary off-shore bar is built up by the storm waves in posi- 

 tion B' ; and afterwards, at times of exceptional storms, successive 

 additions may be made on its outer side, as B". Wind action builds 

 the bar up with dunes, and carries much sand over into the lagoon. 

 But a time will come when the bottom farther to seaward has been 

 deepened enough to enable even the greatest waves to act severely on 

 the outer slope of the bar, taking from it more than they bring to it ; 

 then the outward advance of the bar is changed to a landward retreat, 

 and it is pushed back to such a position as B'". Tliis change in be- 

 havior may be taken to separate the stages of youth and adolescence 

 in the development of a shore line of this kind. 



Young bars that are advancing or that have advanced seaward may 

 often be recognized by belts of dunes, B', B", roughly parallel to the 

 shore, enclosing lines of marsh or " slashes," S, as they are called on 

 the coast of New Jersey. Adolescent bars, retreating landward like 

 B"', may be distinguished by the exposure of the dark mud of the 

 lagoon marsh, M, on their outer slope, as is sufficiently explained by 

 the diagrams. Many examples of this kind miglit be cited. In time, 

 the retreat of the bar will carry it back to the mainland ; then, as long 

 as the marginal cliff is not too high, the dunes, D"", will be heaped 

 directly on the land slope, and the mature stage of shore development 

 is reached. In this stage, the depth of water near the shore is much 

 greater than it was originally ; degradation of the sea floor reaching to 

 depths much below low tide. 



An interesting variation on this type of coastal forms is found on 

 coasts whose submarine slope varies, so that off-shore bars are formed 

 in one district, but an immediate attack is made on the land in a 

 neighboring district. The coast of New Jersey gives a standard ex- 

 ample of this kind. About Atlantic city the bars are built off shore ; 

 about Long Branch, the land is cut back in a retreating cliff of moder- 

 ate height. Although now generally retreating and exposing marsh 

 mud on their ocean side (Ann. Report N. J. Geol. Survey, 1885, p. 

 80 et seQ.), the bars frequently possess dune ridges and slashes, as if 

 they had once advanced seaward. Somewhere in the earlier history 

 of this coast, there must have been a point or fulcrum of no advance 



