7. THE BLACK BELT. 85 



in composition throughout its whole extent and thick- 

 ness. It weathers into a gray clay of exceptional fertil- 

 ity but somewhat difficult to cultivate, because it bakes 

 hard in summer and becomes a very tenacious mud in 

 winter. Chemical analyses of this soil made under Dr. 

 Smith's direction at the time of the Tenth Census show 

 1 to 2 'a of lime, 0.20—0.44% of potash, and 0.10— 

 0.51 7o of phosphoric acid. When the region was first 

 settled much of the soil contained so much organic mat- 

 ter that it was almost black, contrasting with the red 

 soils of neighboring regions, whence the name "black 

 belt." The Lafayette red loam is rather sparsely repre- 

 sented in this region, but where it does occur it usually 

 makes hills, being less easily eroded and dissolved than 

 the Rotten Limestone. Within a few miles of the Ala- 

 bama River in Lowndes and Dallas Counties a considera- 

 ble area is covered with sand which may be even more re- 

 cent than the Lafayette. (The sand-hills near Montgom- 

 ery, mentioned on page 105 of Dr. Mohr's last book, but 

 apparently not identified by previous or subsequent ex- 

 plorers, may be of a similar nature.) 



The soils of the black belt have been described so fully 

 in the publications above cited, and in some of the gov- 

 ernment soil surveys, that it is hardly necessary to give 

 any more details about them here. 



Topography and hydrography. — The Selma Chalk or 

 Rotten Limestone differs from most other limestones in 

 Alabama in that it is almost never hard enough to form 

 steep hills, or pure enough to be dissolved by percolating 

 waters so as to form lime-sinks, caves, subterranean 

 streams and big springs, which are characteristic of so 

 many limestone regions. The prevailing topography is 

 gently undulating, in a manner difficult to describe, 

 though probably due almost wholly to normal erosion 

 processes. Some parts of the region, mostly remote from 

 the rivers, are so level that the railroads have built sev- 

 eral tangents (i. e., straight tracks) a dozen miles or 

 more in length. 



In the spots where the Lafayette sandy loam occurs 

 there has been less erosion than elsewhere, and the con- 

 ical hills formed by this feature have been described by 



