INDUSTRIAL PROGRESS DURING THE YEAR 1875. ccxliii 



when a depth of twenty feet shall have been secured a cer- 

 tain payment shall be made, and so on up to thirty feet ; that 

 twelve months after each of the prescribed depths has 

 been secured a further payment shall be made, provided 

 the same has been maintained during that time ; and that 

 $100,000 shall be paid annually during twenty years, for 

 maintaining the works after construction, and for extending 

 them if necessary, so as to keep the channel at the required 

 depth. The plan of the work is remarkably simple. It con- 

 templates the removal of the point where the sediment of 

 the river is at present deposited, namely, in the shallow 

 water at the entrance of the pass, farther out into the deep 

 water of the Gulf, where filling up again by natural causes 

 will be an indefinitely remote possibility. To accomplish 

 this object, the banks of the pass will be extended, so as to 

 carry the stream far enough out, by the creation of artificial 

 walls within which the waters of the mouth will be confined, 

 said walls being so proportioned in width to the quantity 

 of water escaping as to produce an increased velocity of 

 current, and thus force the stream to scour out for itself 

 a channel of required depth. Extensive lines of jetties 

 will therefore be constructed alons; the course of the mov- 

 ing waters, the jetties being simply dikes or levees un- 

 der water which are intended to act as banks to the river, 

 to prevent it from expanding and diffusing itself as it enters 

 the sea. The greatest difficulties to be overcome were to 

 devise means of creating these artificial walls, and making 

 them secure and permanent upon the exceedingly unstable 

 foundation of soft sediment, into which any works of stone 

 would speedily sink and disappear. Piles alone, or crib- 

 work, however firmly placed, would soon be undermined 

 and swept away by the scour of the current. To meet 

 these difficulties, Captain Eads builds the artificial walls 

 of the river with broad, flat mattresses of willow-brush, se- 

 curely lashed together and anchored to an interior row of 

 piles. The preliminary work is the driving of piles along 

 and inside of the line for the proposed structure. Mean- 

 time great mattresses of willow-brush are constructed, firm- 

 ly locked together with cross-ties and pins. These mat- 

 tresses are towed into position adjoining the piles, and fast- 

 ened to them. If placed at night, by morning the deposit 



