Cross-bedding-sandstone trend relationships in the Chester sandstones of the Illinois basin were investigated jointly by the Kentucky, Indiana, and Illinois State geological surveys. The primary objective of the study was to evaluate cross-bedding as a predictor of regional and local sandstone trends. Determination of the source of the Chester sandstones was a second objective.

Field technique was standardized by the five operators before field work was begun. Altogether, 1,347 cross-bedding observations were obtained from 471 exposures along the 450-mile Chester outcrop of the basin.

A good regional correlation was shown to exist between direction of cross-bedding and major sandstone trends. The typical Chester sandstone trend strikes northeast-southwest and has southwestward-dipping cross-bedding. Detailed studies along the south margin of the basin showed that the directional structures in outcrops of Chester sandstones can be used to predict sandstone trends near the basin margin.

Regional-slope deposits appear to have dominated Chester clastic sedimentation. Most of the Chester sands entered the basin from the northeast.

In the Illinois basin there is evidence that a southwestward-dipping regional slope existed from early Mississippian time into Pennsylvanian time. Approximately 5,000 feet of section that includes important carbonate elements was deposited during this interval. Evidence from the Michigan basin and the northwestern part of the Appalachian basin also supports a late Paleozoic regional slope toward the southwest. Thus over a large part of the north-central states and southeastern Canada the craton sloped toward the southwest in late Paleozoic time.