This datafile shows the general elevation of the top of the New Albany Shale.  These 20- and/or 100-foot isolines were contoured using Esri ArcGIS software.  The contours were created using over data points from the ISGS Oracle database.  The data covers only those portions of the state where the formation is present and does not include any coverage outside of Illinois where the formation may be present.  This data set is intended for use at a scale of 1:100,000 or greater.  These data are appropriate for use in local and regional thematic analysis.  The data are not appropriate as a geodetic, legal or engineering base.