The Sparland cyclothem (Pennsylvanian) occupies an interval from the uppermost part of the Kewanee Group to the lowermost part of the McLeansboro Group in the Illinois basin, and is correlated with part of the Pawnee, Bandera, and Altamont Formations of the Marmaton Group of the Forest City basin. By the use of approximately 1,150 control points, various stages of the cyclothem have been depicted by a series of environmental maps, each map based principally on the distribution of rock types for each stage throughout the area of study.

The Anvil Rock Sandstone is the basal unit in the Illinois basin, and is characterized by a strongly developed pattern of delta distributary channels through which clastics were transported south and southwest from the distant source area on the north and northeast. In the Mid-Continent region, the Mine Creek Shale of the Pawnee Formation is equivalent to the Anvil Rock Sandstone, and contains a less extensive system of channels which indicates the withdrawal of the sea to the deeper parts of the Forest City basin.

Shallow platforms created by Anvil Rock Sandstone bodies in the Illinois basin provided favorable areas for coal-swamp development which led to the formation of the thin sub-Bankston coal of Illinois, and the No. 13 coal of Kentucky. During the succeeding marine incursion, recorded in the Coal City and Bankston Fork Limestones, there was a buildup of the platforms with the result that coal-swamp conditions prevailed on these platforms during the following stage of deposition. The distribution of the Allenby coal of Illinois and the No. 14 coal of Kentucky suggests that many of these platforms in the southern part of the Illinois basin were at depths which were optimum for coal-swamp accumulation. Withdrawal of the sea toward the west caused the development of sandstone channels in sou hern Illinois, which at some locations extend to the level of the Anvil Rock Sandstone; thus all intervening units were removed by erosion. This emphasizes the composite nature of the Sparland cyclothem.

A further withdrawal of the sea toward the west allowed the development of a widespread underclay which formed on deltaic muds in the Illinois basin, and on marine and lagoonal muds in the Illinois basin, and on marine and lagoonal muds in the Mid-Continent region. The widespread extent of the Danville (No. 7) coal of Illinois of the succeeding stage is contrasted to the restriction of the Mulberry coal of the Mid-Continent to narrow bands marginal to the sea. Dark shale above the coal similarly formed throughout the Illinois basin, while regional slope and subsidence variations in the west restricted the development there of dark shale, and allowed the formation of gray shale in waters of normal-marine circulation.

Channel sandstones of the Bandera Shale of the Mid-Continent region, and the overlying Amoret Limestone, correlate with the sub-Piasa shale of Illinois. The latter is a prodelta deposit which exceeds 120 ft in thickness along the Indiana-Illinois border, and which entered the Illinois basin from a distant source area on the north and northeast. The final marine transgression studied is recorded by the Piasa and Worland Limestones, which by their areal extent have proved to be valuable marker beds.