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The Geologic Map of Kentucky was compiled during 1977-78 by R.C. McDowell (project chief), G.J. Grabowski, Jr., and S.L. Moore. McDowell and Moore, both with the U.S. Geological Survey (USGS), had served as field mappers in the USGS-KGS (Kentucky Geological Survey) cooperative mapping project; Grabowski was a geologist with the Kentucky Geological Survey and had conducted stratigraphic studies related to the project.

The base map was prepared by the Topographic Division (now the National Mapping Division) of the U.S. Geological Survey. This was accomplished by producing a mosaic of existing U.S. Geological Survey topographic quadrangle maps, in the 1:250,000 series, with deletion of certain unneeded culture symbols such as schools and airports. Newly built major highways and lakes were added to the base map at a later stage.

Compilation of the geology proceeded in two stages: (1) selection of map units and (2) reduction and transfer of the geologic quadrangle maps to the new topographic base. Selection of units was designed to follow usage on the geologic quadrangle maps, except where the nomenclature had been revised or refined or where later studies provided more detail than shown on the geologic quadrangle maps. Map units were chosen to show the general distribution (and structure) of rock sequences characterized by similar lithology; thus, a thin or restricted but distinctive lithologic unit, such as a "reef," was considered more useful than subdivisions of thicker or more extensive units of the same lithology. However, very thin beds, including coal beds and point localities such as mines, were not plotted because their locations would be too imprecise at the map scale; such features are already well located on the geologic quadrangle maps. Bearing in mind these principles, map unit selection followed four general guidelines: each map unit (1) should be thick enough to be distinguishable at the State map scale, (2) must have been consistently and reliably mapped on all of the geologic quadrangle maps in which it occurs, (3) should, where possible, encompass rocks of similar lithology or common origin, and (4) should, where possible, have distinctive contacts. Initial selection of the map units was made by the compilers and by M.C. Noger of the Kentucky Geological Survey. The list was later modified as a result of consultation with other U.S. Geological Survey and Kentucky Geological Survey geologists. In addition to the stratigraphic units, all known faults except certain minor ones that did not offset contacts were included in the compilation.

As a result of knowledge or perspective gained during the mapping project and in the compilation of the State map, some geologic boundaries have been modified from those shown on some geologic quadrangle maps. These modifications include the following: addition of the upper contact of the Caseyville Formation (Pennsylvanian, western coal basin), provided by T.M. Kehn; revision of the boundary between the Borden Formation and the Fort Payne Formation (Mississippian), by G.J. Grabowski, Jr.; and addition of the Magoffin Member of the Breathitt Formation (Pennsylvanian) in parts of eastern Kentucky, by C.L. Rice. Continuing research has resulted in a few changes in stratigraphic correlations shown on the State map; these are discussed in the pertinent sections that follow.

The transferral of the geologic data from the geologic quadrangle maps to the new base map entailed a reduction of more than 10 times. The most common procedure was to emphasize the faults and contacts to be transferred by tracing over them on the geologic quadrangle maps with a felt-tipped marker pen, followed by photoreduction using a 10-in press camera with a Polaroid adapter. This process, besides being quick and inexpensive, was simple and could be carried out by the compilers. Generally, four quadrangles were photographed at once. The reductions were then placed under scribecoats on which the base map had been imprinted, and the contacts were trace-scribed by the compiler using a rigid graver. An alternate method, which was used for most of sheets 2 and 3, was to scribe the contact on the basis of structure contours transferred to or compiled directly on the base map, a procedure commonly used in compilation of the geologic quadrangle maps. The photoreductions were then used for checking and correction. Primary responsibility for compilation and scribing of the western map sheet (sheet 1) was assigned to Moore; for the central sheet (sheet 2), to Grabowski; and for the eastern sheet (sheet 3), to McDowell.

The scribed contacts, together with the base map, were printed on cronaflex film and hand-colored for checking. These colored cronaflexes were later used as guides for color separation for the published map; the scribecoats produced by the compilers were used in printing as well. Final drafting and preparation of the copy for printing were ably accomplished by or under the competent direction of David L. Oakes of the National Mapping Division of the USGS, in Reston, Va.


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