Description: This datafile shows a generalized depth to the top of the Herrin (No. 6) Coal in Illinois. These 25-foot contours were created by Earthvision software using over 43,900 data points from the ISGS Coal Section stratigraphic database. Because the depth of the coal was contoured directly from drill hole data (as opposed to creating a map of coal elevation and subtracting it from a map of surface topography) the resulting map is essentially based on the assumption that the land surface is a level plain. Consequently, the accuracy of the map is lowest where the coal is shallowest. Limited data were available in the north central, central, and western portions of the state. The data was contoured using fault lines for control and manual adjustments were made to the contours to reflect the presence of known faults. This data set is intended for use at a scale of 1:100,000.
Copyright Text: Data capture, compilation and database maintenance: Marge Bargh, Colin Treworgy, and other ISGS Coal Section staff Compilation and export of data to create this product: Scott Elrick, Blair Tormey, and Chris Korose Documentation: Chris Korose and Andrew Louchios Quality Review: Russ Jacobson, Scott Elrick, and Chris Korose