80 GEOLOGY AND MINERAL RESOURCES OF MISSISSIPPI. 
weather, becomes white as chalk; that at Prairie Rock weathers to a dirty gray and con- 
tains some traces of iron stain on the weathered surfaces. This is due to the oxidation of 
the iron sulphide (pyrite), which is found in small concretions in the fresh rock. 
An analysis of this Prairie Rock limestone, made in the laboratory of the United States 
Geological Survey, follows. It will be seen that the stone is a very pure limestone, in spite 
of the manner in which it discolors on weathering. 
Analysis of Selma limestone from Prairie Rock. 
[By W. S. McNeil.] 
Silica (Si0 2 ) 1. 13 
Alumina (A1 2 3 ) ^ f „ 
Iron oxide (Fe20 3 ) j 
Lime carbonate (CaC0 3 ) 98. 36 
Magnesium carbonate (MgCO :i ) Trace. 
Water 40 
The rock breaks down easily when exposed to the weather, and hence is not now used] 
for extensive building purposes. It is, however, the only road material found in this sec- ] 
tion of the country. It has been used on the road across Boguc Chitto swamp, but is 
unsatisfactory. 
Men familiar with the country say that this hard limestone is very thin — only about 4 feet 
thick — and occurs near the surface. Below this hard stratum comes the soft, whiter "rotten 
limestone," which is, on an average, 20 feet thick and is underlain by the "blue rock," 
which holds water. In digging cisterns, the farmers always dig down to the "blue rock," 
which requires no curbing. 
There are two kinds of soils in the prairie section, giving rise respectively to the "post- 
oak" land and the "prairie" proper. The former is the highest land between the stream 
divides, which has suffered but little erosion. It is very level, sloping gently to the streams. 
This post-oak land is covered with a thin coating of Lafayette clayey sand, never over 10 
feet thick, which has never been all carried away by erosion. The uncleared land produces 
post-oak and some black-oak timber. The "prairie " land is that from which the Lafayette 
has been removed, so that the black, rich loam, formed from the decomposition of the Selma 
chalk, is at the surface. The limestone never comes to the surface except along the streams. 
When the country was first settled this black prairie soil was too strong for cotton. It 
produced a large stalk, but very little cotton. Until recent years all the cotton was planted 
on the poorer " post-oak " lands, and the prairie lands were put in corn. But after years of 
continuous crops of corn the prairie land became the best cotton land, and now the finest 
cotton grows on the prairie lands. 
Later investigation around Columbus and Aberdeen has verified the fact that the land 
known by all as the "post-oak land," as distinguished from the black "prairie soils," is the 
land from which the entire Lafayette has not been removed. The soil is not so rich as the 
prairie soils, and has been largely abandoned for cultivation. 
The following well sections are of interest in this connection: 
Well at Ravine, on land of J. Q. Poind exter. 
Feet. 
Selma chalk 250 
Sand, water bearing, and principal source of water 475 
Red clay 50 
Depth 775 
Water rises within 26 feet of surface. Water soft. 
Well 2 miles due east of Ravine, on Sebe Gavin's land. 
Feet. 
Depth of well 431 
Water flows 16 feet above surface. 
Well on Doctor Patty's land, near Bigbee Valley post-office. 
Feet. 
Depth of well 431 
Water flows 20 feet above surface. Water found in sand, and soft. 
