MISSISSIPPI JETTIES. It is we]] known that the Mississippi River makes its way to the Gulf of Mexico through three great branches or passes.
On the extreme left to the east lies Pass it l'Outre, about 14 miles in length to land's end. In the middle lies South Pass, which, before its improvement, was about 12 miles long. On the right, to the west, lies Southwest Pass, about 17 miles to land's end. In 1875 Congress authorized Capt. James B. Eads to improve the South Pass by the construction of two parallel jetties. The depth between the jetties was required by the contract to be :30 feet, and the Nvidth of the chan nel was required to be 350 feet. The east jetty was made 11,800 feet long from land's end to 30 feet of water in the Gulf; the west jetty was 7800 feet long, and was built 1000 feet from the east jetty and generally parallel with it. The first work was to drive a row of piles spaced 12 feet apart to mark the inner lines of the two jetties. These piles served to guide the operations of sinking the mattresses and were not intended to give strength to the work.
The jetty structures proper consisted of several layers of willow mattresses, loaded down with stone. The first layer was composed of mat
tresses 100 feet long and 50 feet wide. and the succeeding layers of mattresses of the same length, hut decreasing in width to the top mat tress, which was 20 feet wide. Generally four courses or layers of mattresses were sufficient to bring the mattress-work to the water surface. Each mattress was composed of four layers of willow brush. which. when compressed, gave it a thickness of about two feet. The mattresses were character and variable depth of the bar channels has always caused its entrance to be held in terror by mariners and shipowners. To improve these conditions a jetty was completed in 1893 94. Its total length is 4:1.i miles, which makes it the longest jetty in the world. It was con structed by sinking mattresses of brush 3 feet thick and 40 feet wide, and surmounting them by a mound or ridge of rubble-stone. From a low-water depth, generally of 19 feet to 22 feet, in shifting and uncertain channels across the bar, the depth has increased to 29 feet in a single, and, so far, permanent channel.