el] Mississippi. 213 
I sample of Selraa chalk was taken from an old rock quarry situated 
the southwest side of Bogue Chitto Creek, one-half mile east of 
lirie Rock. This limestone differs from that along Oaknoxubee 
er, in the vicinity of Macon, in that it is much harder. In the 
weathered state of the Macon rock, it is very soft and noncrystal- 
line can easily stick a pick into it. But the limestone at Prairie 
:k is a hard so-called "flint rock," crystalline in character, and is 
d for building purposes. The rock at Macon, when exposed to the 
ither, becomes white as chalk, that at Prairie Rock weathers to a 
ty gray and contains some traces of iron stain on the weathered 
faces. This is due to the oxidation of the iron sulphide (pyrite), 
ich is found in small concretions in the fresh rock. 
in analysis of this Prairie Rock limestone, made by W. 8. McNeil, 
;he laboratory of the United States Geological Survey, follows. It 
1 be seen that the stone is a very pure limestone, in spite of the man- 
• in which it discolors on weathering. 
Analysis of Selma limestone from Prairie Rock, Mississippi. 
1 (Si0 2 ) 1. 13 
mina ( A1 2 3 ) 1 
i oxide (Fe 2 3 ) J 
le carbonate (CaC0 3 ) 98. 36 
*nesiinn carbonate ( MgC( ) 3 ) tr. 
ter 40 
Dhe rock breaks down easily when exposed to the weather, and 
ice is not now used for extensive building purposes. It is, however, 
only road material found in this section of the country. It has 
m used on the road across Bogue Chitto swamp, but is unsatisfac- 
y- 
Hen familiar with the country say that this hard limestone is very 
-only about 4 feet thick — and occurs near the surface. Below 
^ hard stratum comes the soft, whiter "rotten limestone," which is, 
an average, 20 feet thick. Below this comes the "blue rock," 
ich holds water. In digging cisterns, the farmers always dig down 
jthe " blue rock," which requires no curbing. 
fhere are two kinds of soils in the prairie section, the " post-oak" 
Id and the "prairie" proper. The former is the highest land 
|ween the stream divides, which has suffered but little erosion. It 
!very level, sloping gently to the streams. This post-oak land is 
jrered with a thin coating of Lafayette, clayey sand, never over 10 
It thick, which has never been all carried away by erosion. The 
icleared land produces post- oak and some black-oak timber. 
The "prairie 1 ' land is that from which the Lafayette has been 
noved, and the black, rich loam, formed from the decomposition 
