226 SEA AND LAND 



entmnce to New York harbor, the direction of motion of 

 the coastal sands is not very definitely determined, the course 

 followed by the tide may be pretty steadily maintained for 

 many years. On the other hand, as on the inlets to the 

 laeoons of the Florida coast, where the march of the sands 

 is tolerably constant, the effect of their movement in altering- 

 the position of the troughs in which tidal rivers flow is often 

 readily observable from year to year. Even a single great 

 storm may bring about very great changes in the position 

 of these channels. 



One of the most interesting features connected with tidal 

 action in the embayed portions of our coast is found in the 

 tendency of the waters when moved by the tidal impulse 

 to organize the flow into regular though sometimes ramifying 

 channels. Rarely if ever do we find the movement diffused 

 as a broad, even sheet over the surface of the embayment ; 

 the flow is along lines determined by accidents, often too 

 slight to escape apprehension. Distinct, more or less sinuous 

 and rather sharp, walled ways are carved, through which the 

 body of the tide passes in flooding and ebbing, and from 

 which and to which the waters move from the higher lying 

 mud flats or marine marshes on either side of the streams. 

 If there be any considerable rivers falling into the harbor a 

 tidal channel commonly extends to the mouth of each stream. 

 These are usually much the deepest and widest, but similar 

 troughs extend into each ramification of the embayment, so 

 that at low tide the basin may appear like a large map of a 

 land river district. It is easy to see how these channels are 

 maintained, though the conditions of their institution are not 

 apparent. They are kept relatively free from sediments by 

 the tide, which, owing to the depth of water, finds less friction 



