RIPLEY FORMATION. 19 
black loam, formed from the decomposition of the Selma chalk, is at the surface. This land 
lies along the slopes or more rolling areas where erosion has been more rapid. 
When the country was first settled the black prairie soil was too strong for cotton. It 
produced a large stalk, but little lint. Until recent years all the cotton was planted on the 
poorer post-oak soils and the prairie lands were put in corn. After years of continuous 
crops of corn the prairie lands became the best cotton lands and now the principal part of 
the cotton is planted on these richer soils. In fact, the thinner post-oak soils in places have 
been abandoned for cultivation and are used only for pasturage. 
At Cliftonville, in northeastern Noxubee County, there is a thin stratum 1 to 6 feet thick 
of hard crystalline limestone similar to that at Prairie Rock. It forms a mesa-like capping 
to the hills in this vicinity. It is locally known as "lime rock," in distinction from the 
" blue rock" below. 
The blue rock of northeastern Noxubee County is the lower subdivision of the Selma. It 
is very rich in lime carbonate and breaks down into a black, easily cultivated, fertile soil 
which produces more cotton and corn to the acre than any other land of the State. The 
higher interstream areas to the west are covered with the post-oak clay soil. 
The sands of the Eutaw formation extend 2 miles west of Aberdeen and the post-oak 
clay soils of the Selma chalk continue westward nearly to the main line of the Mobile and 
Ohio Railroad. Over a large area in central Monroe County the Selma rarely appears at the 
surface, but is always found in wells and cisterns and along the railroad excavations. One 
mile south of Strongs the Illinois Central Railroad has cut into the Selma to a depth of 15 
feet. 
The width of the Selma area is greatest in Monroe and Chickasaw counties, in the latitude 
of Houston. From this locality northward the outcrop becomes narrower and the forma- 
tion thinner. Wells near Rienzi, Corinth, and Wenasoga, Miss., and Chewalla, Tenn., show 
a gradual thinning of the Selma to the north, and it finally disappears completely near Cam- 
den, Tenn. 
RIPLEY FORMATION. 
Immediately above the Selma chalk comes the uppermost division of the Cretaceous, 
which has been called Ripley, from its typical exposure near Ripley, Miss. The materials 
composing this formation are alternating beds of coarse-grained sandstones, limestones, 
clays, unconsolidated sands, phosphatic greensands, and marls. The deep, quiet sea in 
which the great thickness of the homogeneous Selma limestone was deposited became more 
changeable at the beginning of Ripley time. The character of the Ripley deposits marks 
the transition period from the deep, marine deposits of the Selma to the shallow, near- 
shore deposits of the early Tertiary, in which the predominating materials are sand and clays. 
The thickness of the formation, estimated from the width of outcrop, with a westward dip 
of 15 feet per mile, reaches a maximum of 280 feet. 
There is a marked change in topography from the rolling prairies of the Selma to the steep 
hills of the Ripley. The area of the latter is much smaller than that of the Selma. It is 
widest at the north in Tippah County, gradually narrowing to the south, and wedging out 
altogether at Houston, Chickasaw County. To the south the Ripley is well marked in Ala- 
bama, but wedges out in Kemper County, Miss., near Shuqualak. Between this town and 
Houston the Ripley in most places is absent, and when present occurs as outliers. 
Prof. W. N. Logan, of the Agricultural and Mechanical College of Mississippi, in his Geol- 
ogy of Oktibbeha County, page 30, describes three outliers of phosphatic greensand and 
bluish and yellowish micaceous marl which he refers to the Ripley. Exogyra costata, 
Ostreafalcata, Gryphiea convexa, Pecten quinquecostatus, and Placuna scabra are found in the 
marls. Doubtless more detailed work in the various counties along the western border of 
the Selma area would reveal a large number of similar Ripley outcrops. 
The Ripley beds in Mississippi have not received sufficient study and detailed work to 
determine accurately the relative succession of strata. At New Albany and Ecru, which 
are located along the western edge of the formation in Union and Pontotoc counties, there 
