154 TIDES AND CUKRENTS. [CHAP, XXIX. 



line of defence on the part of the pilots, whether for 

 themselves or their friends, is to show that new sand 

 bars are forming, and shoals shifting their places so 

 fast, that no blame attaches to any one for running a 

 vessel aground. To exaggerate, rather than under 

 rate, the quantity of sediment newly deposited by 

 the river, is the bias of each witness, although their 

 statements may in the main be correct ; for in the 

 contest annually carried on between the river and the 

 sea, there is unquestionably a vast amount of de 

 struction and renovation of mud-banks and sand-bars. 

 In these changes the action of the tide, and the 

 power of the breakers during storms, and a strong 

 marine current, all play their part. There seem to 

 be well-authenticated accounts of anchors cast up 

 from a depth of several fathoms near the mouths of 

 the river, and heavy stones sunk sixteen feet deep, 

 arid found afterwards high and dry on shoals. The 

 ballast also of several wrecked vessels, the submer 

 gence of which, in two or three fathoms water, had 

 been ascertained, have in like manner been thrown 

 up, above high water mark, on newly formed islands. 

 All the pilots agree, that when the Mississippi is 

 at its height, it pours several streams of fresh water, 

 tinged with yellow sediment, twelve or more miles 

 into the Gulf, beyond its mouths. These streams 

 floating over the heavier salt water, spread out into 

 broad superficial sheets or layers, which the keels of 

 vessels plough through, turning up a furrow of clear 

 blue water, forming a dark streak in the middle of 

 the ship s wake. I infer, therefore, that both in the 

 summer, when the swollen river is turbid and depo- 



