234 PROCEEDINGS OF THE AMERICAN ACADEMY. 



seems therefore justifiable to infer that iu this locality strong tidal runs 

 have prevented the growth of tombolos. 



The form of the tidal runway is of the indefinite type of channels, 

 called inseqaent by Professor Davis. A broad tidal flat will be cut by 

 runways forming a dendritic drainage pattern (Germ., 5, 36, 37, 79, 80). 

 Where there are large rivers, the pattern of dissection will show the con- 

 trolling influence of the master stream (Germ., 109, 110, 111). 



Ratio betiveen Tides and Currents. — The relative strength of tidal on- 

 and offshore action and alongshore current action is a most important 

 consideration in the determination of the form of coasts. The form of 

 the North Carolina coast indicates that back-set eddies * are relatively 

 stronger than the tides. The prevailing extension of water bodies is 

 along the shore. These alongshore channels or lagoons are connected 

 with the ocean by tidal inlets which cross the bars, and whose position 

 is constantly shifted by alongshore transportation. These inlets repre- 

 sent the weaker tidal intention working at right angles to the general 

 shoreline, while the lagoons indicate the stronger alongshore action. 



Something of the insequent pattern is seen in the ramifying channels 

 inside the offshore bar at Bogue and New River inlets, North Carolina 

 (C. S., 148). Southward along the Carolina coast the alongshore action 

 would appear from the shore forms to diminish in strength in relation to 

 the tidal in- and outflow. 



Series of Forms. — It is possible to arrange shores in a progressive 

 series according to the ratio between tidal on- and offshore and along- 

 shore currents. This series is not one following stages of development, 

 but one which is determined by the ratio between two variables, whose 

 average directions of activity are at right angles to each other. 



The normal development of shorelines as affected b}^ the sea should 

 however be kept in mind, and allowance made in each example for the 

 stage of development indicated. 



When the ratio is in favor of the alongshore current, the forms 

 developed should show extension in the general direction of the shore- 

 line ; when on the other hand the ratio is in favor of the tides, the most 

 pronounced shore feature should be development at right angles to the 

 shoreline. 



Western Florida Type. — On the western shores of Florida, although 

 the tides are weak, the ratio between tide and current action is inferred 

 to be preponderantly in favor of the tidal, as indicated by the form of 



* See page 180, and Bull. G. S. A., 1896, VII. 405. 



