The flow of water between the jetties has been increased by temporary constructions, such as sheet piling and wooden aprons; a dam turns the•wide• from Grand bayou into the pass; and dikes at the head of the pass still farther increase the flow. Max E. Schmidt, cm, one of the assistant engineers, says:. " There were three destructive ele ments to be overcome by these works: 1. The abrading power of the river current; 2. The momentum and impact of the waves; 3. The underminin; power of the waves. With a full appreciation of the magnitude of these forces, no design was made, nor was any detail allowed to be put into tire works, which did not strictly adhere to the follow ing practical laws: 1. That a broad and elastic foundation prevent undermining; 2. that proper slopes will resist impact of the waves; 3. That tight work will stop leakage; en I 4. That work maintained at a uniform height will obstruct the escape of water by overflow." Noting in their order how far these laws have been fulfilled, we see, 1. That the two rows of mattresses, which have sunk into the bottom till in firmer strata was reached, afford a secure foundation; 2. Where the jetties pierce the bar, deposits on the sea side give ample protection. while, on the river side, wing dams—projecting perpen dicularly 150 ft. from the jetties—stopped the currbnt and caused sediments to be depos ited, producing a gentler and more resisting slope, with a simultaneous deepening of channel: at tire gulf ends of the jetties and extending some distance towards shore, the slopes have been improved by sinking cribs of pahnetto wood at both sides of the mattresses, and then building up the desired slope with stones. 3. The compression of
the mattresses by the weight of stone. and tire infiltration of sand has done much to dimin ish the leakage, but more time is needed to completely fig interstices, and the use of gravel and broken stone near the jetty top will greatly assist. 4. The shore jetty sec tions are now maintained, above high-water mark without difficulty. Upon the summit of the gulf sections a continuous embankment of concrete, varying in dimensions, but usually 12 ft wide and 33,- ft. thick, has been constructed for a distance of 3,800 ft. upon the east jetty, and 2,800 ft. upon the west jetty. The concrete was molded in blocks weigh big from 25 to 72 tons, and these were cemented together afterwards, forming one solid stile of great resisting power on each jetty, and aiding in the diminution of leakage by compressing the mattresses; it is hoped that the weight will cause the elastic limit of the wilinivs to be reached, thus increasing its impermeability. A massive parapet is to sur mount the concrete, the time of construction at any point depending upon the subsi dence of the jetties. July 10, 1879, capt. Ends reported the completion of the jetty Work; depth through the jetties over 30 ft.; at the head of the pass, 26 ft.—measure ments being taken with the river at its lowest stage. The improvement of harbors by jetties depends upon the general principles cited as applicable in the great works at the mouth of the Mississippi; and many harbors on the great lakes and elsewhere in the United States have been thus made more accessible.