Type designation:

Type locality: The name “Anvil Rock” was used by Owen (1856, p. 45), for a natural feature of sandstone shaped like an anvil near Dekoven, Union County, Kentucky 2,750 ft (0.84 km) from the east line and 1,100 ft (0.34 km) from the south line, N-17, Carter coordinates) (Ault, 1986).

Reference Section: The cored interval from 538 to 561 ft (164 to 171 m) in Indiana Geological Survey drill hole (SDH) 285 (Indiana Geological Survey Petroleum Database Management System No. 110813), SE¼NE¼SE¼ sec. 35, T. 5 S., R. 14 W., Posey County, was designated as an Indiana reference section for the Anvil Rock Sandstone Member by Ault (1986).

History of usage:

Extended: The name “Anvil Rock Sandstone Member” was adopted for use in Indiana by Ault (1986).

Assignment: The Anvil Rock Sandstone Member was assigned to the Dugger Formation by Ault (1986).


The Anvil Rock sandstone was mapped in Illinois, Kentucky, and Indiana by Hopkins (1958). Unpublished mapping by Curtis H. Ault in Posey County and by Donald L. Eggert in Gibson County indicates that the Anvil Rock is present in these counties as channel fill and also as a thin sheet in many places (Ault, 1986).

Only a few cores of the Anvil Rock Sandstone Member are available in Posey and Gibson Counties, and detailed petrography of the sandstone is not well known for the subsurface in Indiana (Ault, 1986). In the reference core, SDH 285 in Posey County, the unit consists of a siltstone and very fine grained to fine-grained sandstone that is gray to light gray and cross bedded in part (Ault, 1986).

Th sandstone is 0 to 20 ft (0 to 6.1 m) thick in much of Posey, Gibson, and Knox Counties (Hopkins, 1958). In a major channel that trends generally northeast-southwest in northwestern Posey County, western Gibson County, and southwestern Knox County, the sandstone ranges upward to 81 to 160 ft (24.7 to 48.8 m) in thickness (Hopkins, 1958, plate 1; Ault, 1986). In a second channel filled with Anvil Rock that has been mapped in eastern Posey County and extends southward into Kentucky, the sandstone can range upward to 41 to 80 ft (12.5 to 24 m) in thickness (Hopkins, 1958, plate 1).


The sheet phase of the Anvil Rock sandstone underlies a gray shale below the Universal Limestone Member and overlies a gray shale above the Hymera Coal and Providence Limestone Members, all of the Dugger Formation (Ault, 1986). In Posey County, channels filled with Anvil Rock sandstone have been cut through underlying members of the Dugger to within about 30 ft (9 m) of the Springfield Coal Member (Petersburg Formation) (Ault, 1986).


Part of the Anvil Rock Sandstone Member occupies the same stratigraphic position as the Bridge Junction Sandstone Member mapped by Friedman (1989) in parts of Vigo County, Indiana (Ault, 1986). No direct correlation between the sandstones, however, has yet been shown, although they may be the same sandstone (Ault, 1986).

Regional Indiana usage:

Illinois Basin (COSUNA 11)
Supergroup: none
Group: Carbondale Group
Formation: Dugger Formation
Member: Anvil Rock Sandstone Member

Misc/Abandoned Names:


Geologic Map Unit Designation:


Note: Hansen (1991, p. 52) in Suggestions to authors of the reports of the United States Geological Survey noted that letter symbols for map units are considered to be unique to each geologic map and that adjacent maps do not necessarily need to use the same symbols for the same map unit. Therefore, map unit abbreviations in the Indiana Geologic Names Information System should be regarded simply as recommendations.

COSUNA areas and regional terminology

Names for geologic units vary across Indiana. The Midwestern Basin and Arches Region COSUNA chart (Shaver, 1984) was developed to strategically document such variations in terminology. The geologic map (below left) is derived from this chart and provides an index to the five defined COSUNA regions in Indiana. The regions are generally based on regional bedrock outcrop patterns and major structural features in Indiana. (Click the maps below to view more detailed maps of COSUNA regions and major structural features in Indiana.)

COSUNA areas and numbers that approximate regional bedrock outcrop patterns and major structural featuers in Indiana.

Major tectonic features that affect bedrock geology in Indiana.

See also:

Bridge Junction Sandstone Member


Ault, C. H., 1986, Anvil Rock Sandstone Member, in Shaver, R. H., Ault, C. H., Burger, A. M., Carr, D. D., Droste, J. B., Eggert, D. L., Gray, H. H., Harper, Denver, Hasenmueller, N. R., Hasenmueller, W. A., Horowitz, A. S., Hutchison, H. C., Keith, B. D., Keller, S. J., Patton, J. B., Rexroad, C. B., and Wier, C. E., Compendium of Paleozoic rock-unit stratigraphy in Indiana–a revision: Indiana Geological Survey Bulletin 59, p. 6.

Friedman, S. A., 1989, Geology and coal deposits of the Clinton area, west-central Indiana: Indiana Geological Survey Special Report 42, 50 p.

Hansen, W. R., 1991, Suggestions to authors of the reports of the United States Geological Survey (7th ed.): Washington, D.C., U.S. Geological Survey, 289 p.

Hopkins, M. E., 1958, Geology and petrology of the Anvil Rock Sandstone of southern Illinois: Illinois State Geological Survey Circular 256, 49 p.

Owen, D. D., 1856, Report of the geological survey in Kentucky, made during the years 1854 and 1855: Frankfort, Ky., 416 p.

Shaver, R. H., coordinator, 1984, Midwestern basin and arches region–correlation of stratigraphic units in North America (COSUNA): American Association of Petroleum Geologists Correlation Chart Series.

For additional information contact:

Nancy Hasenmueller (
Date last revised: July 28, 2017