DRAINAGE OF WET LANDS OF SOUTHERN LOUISIANA. 9 



Bayou L'Ourse is an insignificant stream, occupying the center of a long and 

 important ridge. It is probable that at one time this bayou served as an out- 

 let for the Lafourche or possibly of some predecessor of the latter bayou, 

 draining in a more easterly direction through Bayou Blue, Lake Fields, and 

 Long Lake. Wax and Little Wax Bayous are streams of erosion rather than 

 of sedimentation and have been formed wholly or in part by the action of 

 storms and the tidal flow which is quite strong along this portion of the 

 coast. As a result, the bayous are bordered by the marsh or by very low ridges. 

 Both streams are from 10 to 50 feet in depth and 100 to 200 feet in width. 1 



In addition to the above, Bayous Terrebonne and Black, in Terrebonne Parish, 

 are typical examples of the sedimentation type, while Bayou des Allemands, the 

 connection between Lake Des Allemands and Lake Salvador, is an excellent 

 illustration of the tidal-erosion type. 



From the foregoing it may be seen that the chief difference between the 

 various types of soils is the variation in fineness of material, rather than differ- 

 ence in chemical composition. 



CLASSIFICATION AND EXTENT OF SOILS. 



The various types of soil grade imperceptibly into one another, but the fol- 

 lowing classifications have been made by the Bureau of Soils of this department : 

 Yazoo sandy loam, Yazoo loam, Yazoo clay, Sharkey clay, muck, and Galveston 

 clay. 



The first three classes are ridge soils and are limited in extent, forming a 

 very small percentage of the total area. These soils have sufficient elevation 

 to drain naturally, and as they are practically all well drained and cultivated 

 no discussion of them will be given. For additional information the reader is 

 referred to the publications of the Bureau of Soils. 



The last three classes include practically all the undrained soils of this 

 section. The Bureau of Soils says of this first type : 2 



The Sharkey clay is the heaviest soil of the New Orleans area. It is the 

 most extensive type and as only a small proportion of it is under cultivation, 

 the subject of the reclamation of the large unused area is attracting consider- 

 able attention. 



The soil is a heavy black clay to a depth of 5 or 6 inches. The dark color 

 is due to the large content of organic matter which has been derived from the 

 heavy growth of vegetation as the clay was slowly deposited. This decayed 

 vegetation has had a marked beneficial effect on the structure of the soil by 

 causing it to break under the plow into little blocks and to assume a much 

 more favorable condition than is usually possible with this type. The subsoil 

 is a brown or drab waxy clay of a most impervious and tenacious character. 

 The percentage of organic matter is much smaller than that of the soil. 



The Sharkey clay shrinks greatly upon drying, and the surface of a drying 

 field is always checked by large sun cracks. 



The Sharkey clay occupies the entire land surface of the area, with the ex- 

 ception of narrow strips along the rivers and bayous, where the swifter over- 

 flow waters have built up natural levees of coarser sediments, and excepting 

 also considerable areas where it has been covered so completely by decayed 

 vegetation that a muck type has been established. * * * The Sharkey clay 

 areas are for the most part forested. The exceptions are those comparatively 

 small areas in cultivation and the treeless prairies which cover a considerable 

 area in the southern part of the present survey. In the very wet, poorly drained 

 tracts there is an almost impenetrable growth of cypress, willow, maple, water 

 oak, and sometimes ash. On the better drained portions the woods are more 

 open and the palmetto flourishes near the border. 



Of the soil classed as muck, the Bureau of Soils says : 3 



Between the Mississippi River and Lake Pontchartrain are extensive areas 

 where the dense growth of vegetation has decayed and accumulated on the sur- 



1 Manuscript report of A. M. Shaw. 



2 U. S. Dept. Agr., Field Operations of the Bureau of Soils, 1903, p. 451. 



3 U. S. Dept. Agr., Field Operations of the Bureau of Soils, 1903, pp. 452, 453. 



25102°— Bull. 71—14 2 



