704 HERDMAN F. CLELAND 



high — of chalky limestone, and the tributary streams have all the 

 characteristics of youth. 



The sides of the Black Belt trough are bounded on the north 

 and south by ridges, formed of the more resistant strata of the 

 Coastal Plain, which rise 200 ta 300 feet above the general level 

 of the surface. The pronounced cuesta which forms the southern 

 border of the trough is composed of the sandy, more resistant 

 Ripley (Cretaceous) sediments. 



The Black Belt, Black Prairie, Cotton Belt, or Cane Brake, 

 as it has been variously called, can be briefly described as a belt of 

 rich, black soil with an average width of 20 to 25 miles, and an 

 area in Alabama of about 4,300 square miles. It extends in an 

 east-west direction in south central Alabama and conforms 

 exactly with an easily decomposed, impure, chalky limestone of 

 rather uniform composition (Selma chalk) which has a thickness 

 of about 1,000 feet in the western part of the state and thins out 

 and disappears in the east near Montgomery. This formation 

 dips to the south at the rate of 30 to 40 feet to the mile while the 

 surface slopes at a much less rapid rate in the same direction. It 

 is the weathering of the beveled edges of this limestone that 

 determines the width and position of the Black Belt. The soil 

 formed from this rock is a clay of exceptional fertility but some- 

 what difficult to cultivate because it bakes in summer and 

 becomes tenacious mud in winter. 



After the deposition of the Coastal Plain sediments a deposit 

 of red sandy loam, called the Lafayette formation, was laid down 

 on them, either during the early Pleistocene or near the close of 

 the Pliocene, and formed a veritable mantle covering many hun- 

 dreds of square miles. The depth of this formation is, in places, 

 as much as fifty feet, but little of it has a thickness of more than 

 25 feet. The origin of the Lafayette has given rise to much dis- 

 cussion,^ but as the underlying formations in Alabama contain little 

 quartz from which pebbles could be made, the abundant water- 

 worn quartz pebbles show that in this state, at least, it must have 

 been transported long distances. On the sides of the Black Belt 

 trough some knobs and ridges are capped by this deposit, proving 

 W. W. Shaw, U.S. Prof. Paper 108 H. 



