Description: <DIV STYLE="text-align:Left;"><DIV><P><SPAN>This data set is a polygon coverage of the cumulative overburden of North-Zone 9, in feet, over extent of the North-Zone 9 coal and its horizon (stratigraphic equivalent) in Central Texas only. The coverage was produced by gridding more than 28,500 public and confidential point- source data from the National Coal Resources Data System (NCRDS) of the USGS, using EarthVision (Version 4.0.2) software, subsequently contoured into 6-inch intervals, and imported to ARC/INFO. The 'overburden' item for each polygon reflects a value in feet halfway between the bounding contour lines. This value represents results of gridding which averages point values within cells, therefore, public point data may not always match values represented in the overburden data layer.</SPAN></P></DIV></DIV>
Copyright Text: The stratigraphic data stored in the NCRDS has been submitted by State Geological Surveys and USGS scientists since its inception in the middle 1970's through state cooperative programs. The data for the North-Zone 9 coal bed was used with the permission and through the cooperation of coal geologists (primary contacts listed) at the State of Texas Bureau of Economic Geology and the State of Texas Railroad Commission