CARBONIFEROUS.
Mississippian or Lower Carboniferous.—At the close of the Devonian that portion of the State south of the latitude named received a heavy deposit of limestones, sandstones, and shales aggregating 150 to 200 feet in thickness, called the Lower Carboniferous or. Mississippian series. Worthen divides this series into five groups as follows : Kinderhook, mostly shales and limestones, 100 to 150 feet; Burlington, massive lime stone, usually excellent as a building stone, 50 to 200 feet; Keokuk, mas sive limestone below, passing into shales in the upper portion, 150 feet; St. Louis, mostly heavy bedded argillaceous limestone, 100 to 200 feet thick, passing locally into shales on one hand and a fine quality of polite on the other, and Chester, consisting of heavy beds of sandstones and limestones with some shales, in all 500 to 800 feet thick.
The Lower Carboniferous forms the bluffs of the.Mississippi and a variable belt to the eastward from the southern portion of Mercer county 'to Alexander county and a considerable part of the Ozark ridge across the State. It is believed to underlie all the central and southern part of the State, and well records indicate that it increases in thickness and be comes more shaly towards the .eastern border. Present information seems
to indicate that the Chester does not occur north of a line drawn through Litchfield and Danville.
Pennsylvanian or Coal Measures.—For a long time subsequent to the deposition of the Lower Carboniferous, that portion of the State between the latitudes of LaSalle and Carbondale oscillated between a slightly ele vated condition, in which extensive marshes and lakes were interspersed between areas of higher drier land, and a condition in which the entire area was covered by the waters of a shallow sea in which beds of shale and sandstone 20 to 200 feet thick and occasional thin beds of limestone accumulated. These conditions alternated many times with the result that a formation now 50 to 1200 feet thick was built up in this portion of the State. In the marshes and lakes great beds of vegetable matter accumulated, which were afterward converted by the pressure of subse quent deposits into bituminous coal, and beds of this material are now found intercalated in the sandstones and shales before mentioned.