TOPOGRAPHY. The highest ridges, in Claiborne and Union parishes, rise to 500 feet above the sea. The land slopes almost imperceptibly to the southeast. The bottom lands of the Missis sippi River at the Arkansas line have an eleva tion of 130 feet, at Natehez 66 feet, at Baton Rouge 34 feet. at New Orleans 15 feet. The average elevation of the State is only about 75 feet above sea level. All the rivers have flood plains of generous width, more or less liable to inundation at times of high water. These bottom lands. in the ease of the Red and Ouachita (Wash ita) rivers, average 10 miles in width; on the Mis sissippi River. from 10 to 60 miles. Through these flood plains the rivers meander on a de creasing gradient, constantly depositing their loads of silt. This results in building up their beds. until the river flows at the summit of a ridge. From the river edge the land slopes away with a gentle gradient of about seven feet in the first mile. then with only six inches per mile to the marshes and bayous of the outer margin of the flood plains. These river margins furnish a soil of inexhaustible fertility and are largely utilized for plantations of cotton and sugar cane. They are protected from overflow by artificial banks or levees of varying height. there being over 1500 mile: of such levees in Louisiana. Occasion ally at times of great flood the levees give way in places, the 'crevasse' allowing the river to over flow the adjacent bottom, and carrying destruc• tion far and wide. The Gulf margin exten hint :about sixty miles inland consists of a marshy plain. the Only land being the raised river mar gins and occasional small patches of prairie and live-oak ridges, the prairie area increasing to the west. This lowland and the river bottoms cover an area of 19.200 square miles, or a little less than one-half the area of the State.
The principal rivers are the Mississippi, which flows 600 miles through the State and along its borders, the Red, ouachita.Sabine.and l'earl; awl all of these are navigable at all stages of water. Most of the large rivers of the lowland region are distributaries of the Mississippi and Red rivers, locally called bayous. and nearly all are
navigable. They interlace all over the area in the most bewildering fashion. The most impor tant ones are Atehafalaya Bayou. Bayou la Fourche, and Bayou Bumf. The:e bayous are very active in taking off the excess water in time of flood.
The lakes are of three classes: First, those of the coastal margin—Pontchartrain. Borgne. Maur, pas. Sabine, and many others; they are merely parts of the submerged coastal plain which have escaped tilling by delta action. They have salt or brackish water and their level rises and falls with the tide. Second. a host of crescent lake-, oxbow lakes as they are called, which are the unfilled portion of amputated and abandoned meanders. They are usually connected with the river at the loNver end by a bayou. The third class of lakes is found in the tributaries of the Red River in the vieinity of Shreveport. and are due to the more rapid silting up of the channel of the master stream than of its tributaries. thus drowning the lower courses of the lateral streams. The main body of the delta proper of the great river extends about seventy miles beyond the gen eral trend of the Gulf coast, while the rennaer passes advance about 35 miles still farther into the Gulf.
The great delta is rapidly advancing into the Gulf, depositing in excess of the waste of the waves and of a possible sinking of the immediate region, and it gives promise of annexing the Mobile system in the immediate geologic future, The rapid silting in the passes leaves a maximum depth at the outer bar of only twelve feet, though the main river has a depth of WO from the mouth of the Red 11iver down to tl e passes. Capt. J. B. Lads was a ppnlIlied In the CrOVV111111e1II in 1H75 to construct artificial banks or jetties in the passes, narrowing the stream ..-I compelling it to corrade a deep channel and to keep it open. It was a complete siteeess. a thirty foot channel having been maintained ever since, so admitting vessels of the largest class to the port of New Orleans.