418 



F. P. GULLIVER — CUSPATE FORELANDS. 



been used, but the rivers in entering the sea often do aid in the con- 

 struction of cuspate projections from the older mainland, and this class 

 of forelands will now be considered. 



RIVER VERSUS CURRENT. 



When a river empties into the sea a contest ensues between it and the 

 currents, except where the sea is at work upon an offshore bar and the 

 river mouths in a protected lagoon. The river transports waste to sea- 

 level, the currents transport it beyond wave attack or Ijelow wave-base. 

 At the shore therefore the river intention and the sea intention are op- 

 posed to each other. The river tries to build forward its delta, while the 



sea attempts to cut into the land. If the river in- 

 tention is successful a lobate delta results. If the 

 sea carries out its desire no delta is constructed, 

 the complete satisfaction of the sea being shown 

 where the river is blocked by tlie beach, the water 

 having to filter through the sand, as is the case at 

 Oceanside, California. A great variety of interme- 

 diate forms of deltas occur, which are determined 

 by the arrangement and the ratio between river 

 and sea activity. One where both agents are effec- 

 tive is the cuspate delta. 



THEORY OF FORMATION. 



Three hypotheses for the formation of cuspate 

 deltas will be here presented. The first (figure 10) 

 is where the river mouths in a locality where the 

 dominant sea action is on and off* shore. The cur- 

 FiGVKK io.~/d,aisiagrsoj- ^^^^^ flowing toward the land jvill fiow to the right 

 Delta GroiLth, with dominant and left of the moutli of the strcaui, carrying the 



on and off shore Currents. • ii*i i. ixi "i i ii-it 



river detritus toward the mainland and huildmg 

 oat the foreland. The outflowing current will doubtless carry some 

 material back from the land, but according to tliis theory of growth the 

 foreland is built up mainly from the land waste brouglit down by the 

 river and from bottom detritus brought inshore by the currents. 



The second hypothesis is where the dominant action is- alongshore. 

 As indicated in figure 11, the current is from the right. In the earlier 

 stages of this method of growth the alongshore current, if relativel}'' 

 stronger than the river current, will curve around the mouth of the river 

 and give the delta a rounded outline. As the delta grows forward it be- 

 comes more difficult for the alongshore current to bend around the point 

 of the delta, and finally it is broken into two eddies, as shown in the out- 



