4 SOILS OF THE EASTERN UNITED STATES. 



when the moisture condition is exactly right, this granulation is 

 promoted and an exceUent surface tilth may be secured. 



The Houston black clay is easily distinguishable from all other 

 upland soils within the Coastal Plain region. Its distinctive black 

 coloration, its waxy nature, and its obvious derivation from the 

 underlying white, gray, or blue marl are all characteristic of this type. 

 It is the only extensive black clay soil of the upland region. 



SURFACE FEATURES AND DRAINAGE. 



Characteristically the Houston black clay occupies the nearly level 

 or gently undulating prairies of southern Oklahoma and central 

 Texas. These regions have a distinct relief when viewed broadly. 

 Any single square mile of the prairie country is almost absolutely 

 level, or only gently sloping, but when an area the size of a county is 

 considered, it will be found to consist of broad gently sloping ridges 

 separated by shallow nearly level hollows or slightly sloping valleys. 

 There are no pronounced elevations and no steep slopes within the 

 area of these prairies. The major streams, which flow from the inland 

 region to the seacoast, have frequently cut broad, rather shallow 

 trenches through the surface of the land, along whose margins erosion 

 has in places cut back gullies to a distance of several miles. It is 

 within such areas that the chief topographic breaks within the surface 

 of the prairie occur, and where the principal danger from erosion is 

 encountered in the cultivation of the type. 



The Houston black clay is. fairly well drained in all of the areas 

 where it occurs. Only the more level tracts occupying the depres- 

 sions between the higher ridges are found lacking in this respect. 

 The subsoil drainage is not always so good. The stiff, waxy plastic 

 subsoil retains large amounts of soil moisture, and as a result, upon 

 the most level areas it is frequently the case that the natural internal 

 drainage of this type should be supplemented by the installation of 

 tile drainage systems. This applies particularly to those portions of 

 the type which lie in the more humid region of its occurrence. 



Erosion is not a serious feature in the cultivation of the Houston 

 black clay, with the exception of limited areas where the main 

 upland portion of the type is intersected by the major streams or their 

 tributaries. In such localities, to a limited extent, erosion along the 

 steeply sloping stream banks and smaller gullies is sometimes serious 

 upon the individual farm, although nearly negligible so far as the 

 entire extent of the type is concerned. 



LIMITATIONS IN USE. 



The Houston black clay is probably the stiffest and most tenacious 

 upland soil among those generally used for agricultural purposes in the 

 Gulf States. Its texture and even its characteristic structure are such 



