VI. OF THE FLOOD TIDE. 7 



wood for example, be thrown into the water at the first point, but at a distance from 

 tlie shore, the action of the flood will tend to make it approach the shore, carrying 

 it forwards at the same time in the direction of its course. It will finally reach the 

 shore, upon which it will rise with the surface of the water, and there it will ulti- 

 mately be left. "When the flood tide changes to ebb, and runs in the opposite direc- 

 tion from B to A, preserving apparently an opposite course, and seeming to adhere 

 not less closely to the shore, this piece of wood will not be disturbed, but will remain 

 in the place at which it was left by the flood tide ; and if the flood of the next day 

 should rise higher vijion the shore than its predecessor, the piece of wood will be 

 lifted still farther up, and again left. And if the floating object should be im- 

 mersed, so that a part of it will be under the surface, or should be suspended under 

 the water by means of a float, the result will be the same. 



And again, if a strong wind should arise from such a quarter as to cause a heavy 

 sea upon the beach, to create a surf, the floating body will be thrown up still farther 

 on the shore ; if it be light, to the farthest line to which the surf reaches ; if heavy, 

 not so far, perhaps, but that the inner edge of the waves may still break over it. 

 These are the general facts, of which I wdll directly cite some examples that have 

 fallen under the notice of the most casual observer. 



And to these may be added one other, that is, if during the ebb tide a floating 

 object be placed upon the water, outside of the line at which the sea breaks, it will 

 be taken off, but if inside the breakers, it will be cast upon the shore, and there left. 



From these facts it appears that there is a mechanical action by means of which 

 the water, when in contact with the shore, ejects the substances either floating upon 

 its surface, or held by it in suspension, and that the effect of the flood current is to 

 transport these substances and place them within the reach of this action, and that 

 of the ebb is to transport these substances beyond the reach of this action. That 

 is to say, what is called the law of deposit of the flood tide may be divided into 

 two distinct phenomena ; one of which is the transporting power of the flood cur- 

 rent towards, and on to, the shore, the other the dynamical action of the water at 

 the shore. 



Concerning the first of these, the transporting power of the flood current towards 

 the shore, which acts equally upon objects on, and below the surface, it is important 

 to bear in mind the service it performs in bringing all suspended matter within reach 

 of the latter power, particularly on an alluvial coast where, in consequence of the 

 destructive agency of stonns, great quantities of sand, &c., are continually placed at 

 its disposal. It will be observed that I make here an entire distinction between 

 tidal waves and tidal currents. "What the effect, or modus operandi, of the oceanic 

 tidal wave might be, if it were permitted to approach a coast without interruption 

 or interference, until it actually impinged upon the continent, will appear hereafter. 

 This, however, is a case not found in nature. Owing to the rapid decrease of depth 

 near the land, and to the broken and indented fomis of coasts, the water, the sur- 

 face of which is raised by the transmitted wave, accumulates, and overflows in every 

 direction, giving rise to currents which, more or less rapid, constitute one of the 

 general features and characteristic conditions of the tides. These currents, though 

 generally appearing to run along the land on the external sea border, do actually 



