682 



DYNAMICAL GEOLOGY. 



only little of what fell over the flats), and bears it to the ocean. Here, 



the current loses much of its ve- 



Fig. 1099. 



Fluvio-marine formation along the coast of 

 North Carolina : CK, Currituck Inlet (to Cur- 

 rituck Sound) ; N, New Inlet ; H, Cape Hat- 

 teras ; 0, Ocracock Inlet ; C, Cove Inlet ; L, 

 Cape Lookout. 



locity, in the face of the waves, 

 and with the spreading of the wa- 

 ters ; and hence a deposition of de- 

 tritus goes on in the shallow sea, off 

 the mouth of the stream ; and this 

 continues until the tide stops anew 

 the flow of the fresh- water stream. 

 Between the tidal currents, espe- 

 cially the in-flowing, and the river, 

 there is a region of comparative 

 equilibrium in the two movements ; 

 and there the accumulations of 

 sand or detritus take place, form- 

 ing sand-bars. 



Humphreys and Abbot observe, in speak- 

 ing of the Mississippi delta, that, as the 

 river-water rises above the saltwater, from 

 its low density, there is a dead angle be- 

 tween the two. The current out of the 

 Passes pushes sand and earth before it, 

 until, reaching, it begins to descend upon 

 the salt water of the Gulf; and here this 

 material " is left upon the bottom, in the 

 dead angle of salt water. A deposit is thus 

 formed, whose surface is along or near the 

 line upon which the fresh water rises on 

 the salt water, as it enters the Gulf; and 

 this action produces the bar." 



Whenever there is a tidal movement along a coast the depositions 

 from the discharging rivers will be most largely made against or to- 

 ward the cape facing the incoming tide ; that is, the western cape or 

 side, in case the tidal movement is westward. If in such a case, the 

 eastern or opposite side has a long projecting cape or breakwater, there 

 will be the best possible conditions in the outline of the coast for re- 

 taining an unobstructed entrance. The long outstretching cape keeps 

 the tidal current far out, so that the detritus cannot be driven into the 

 mouth of the stream, but only to the western cape and to the shores 

 and reefs farther west ; a comparatively small stream may keep clear 

 the channel of a bay so favored. But with the longer cape on the 

 other side, the mouth of the river would be wide open to the incoming 

 tide, and into it all the detritus would be thrown to choke it ; conse- 

 quently great reefs clog the entrance. Only a very large river could 

 succeed in keeping open a deep channel under such conditions. The 

 Connecticut River fails badly. 



