Type designation:

Type locality: The Sample Formation was originally named the "Sample Sandstone Member of the Gasper Oolite" by Butts (1917, p. 70-73), who designated a type locality at Sample Station, Breckinridge County, Kentucky (Gray, 1970, 1986). As exposed in that area, the formation consists of 20 to 40 ft (6 to 12 m) of massive thick-bedded and cross-bedded sandstone, flaggy sandstone, and shale (Gray, 1970, 1986).

Reference section: A railroad cut near Huron, Lawrence County (Gray and others, 1957, p. 10-14; Malott, 1952, p. 103-105), was designated a reference section for the Sample Formation in Indiana (Gray, 1970, 1986).

History of usage:

Equivalent rocks in Indiana were originally given the name “Brandy Run Sandstone” (Malott, 1919, p. 10; Gray, 1970; 1986). This name was abandoned when equivalence to the Sample Sandstone was recognized (Cumings, 1922, p. 515-516; Gray, 1970; 1986). Dominance of sandstone on natural outcrops gives a false impression of the lithology of the unit, as is also true for other Chesterian clastic units, and for this reason Gray and Perry (1956) changed the name to Sample Formation (Gray, 1986).


The Sample Formation in Indiana is 15 to 50 ft (5 to 15 m) thick and consists of varicolored shale and thin-bedded and cross-bedded sandstone (Gray and others, 1957, pl. 2; Gray, 1986). Shale dominates in the northern part of the outcrop area from Putnam County southward through Orange County, but sandstone becomes more conspicuous southward to the Ohio River (Malott, 1952, p. 13; Gray, 1970; 1986).

Distribution: The formation is present in the subsurface from Parke County southwestward, but in much of this area it is indistinguishable from formations above and below because the limestone formations that define its upper and lower boundaries are absent (Sullivan, 1972, p. 19; see also the discussion of the West Baden clastic belt under Elwren Formation) (Gray, 1970; 1986).


The Sample Formation conformably overlies the Beaver Bend Limestone and is overlain conformably by the Reelsville Limestone (Gray, 1970; 1986). Where the Reelsville is depositionally absent, clastic rocks that would normally be assigned to the Elwren Formation directly overlie clastic rocks that would normally be assigned to the Sample, and to place a contact between them is difficult or impossible (Gray, 1970; 1986). At a few localities a disconformity appears to separate the two formations (Malott, 1919, p. 11; 1952, p. 56-57; Gray, 1970; 1986), but Gray and Perry (1956) considered this feature to be of local significance only, a manifestation of what later came to be understood as the West Baden clastic belt (Gray, 1986). Where higher Chesterian rocks are missing as a result of pre-Pennsylvanian erosion, the Sample Formation is disconformably overlain by the Mansfield Formation (Morrowan) (Gray, 1986).


The Sample Formation has been considered equivalent to part of the Paint Creek Formation of former Illinois usage (Swann and Atherton, 1948, p. 270) (Gray, 1970; 1986). The name “Paint Creek” has been replaced in the standard Chesterian section, however, and the Sample is now designated as the middle member of the Ridenhower Formation (Swann, 1963, p. 35; Atherton and others, 1975, p. 154) (Gray, 1970; 1986).

Regional Indiana usage:

Illinois Basin (COSUNA 11)
Supergroup: none
Group: West Baden Group
Formation: Sample Formation
Illinois Basin Margin (COSUNA 12)
Supergroup: none
Group: West Baden Group
Formation: Sample Formation

Misc/Abandoned Names:

Brandy Run Sandstone

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.


Atherton, Elwood, Collinson, Charles, and Lineback, J. A., 1975, Mississippian System, in Willman, H. B., Atherton, Elwood, Buschbach, T. C., Collinson, Charles, Frye, J. C., Hopkins, M. E., Lineback, J. A., and Simon, J. A., Handbook of Illinois stratigraphy: Illinois State Geological Survey Bulletin 95, p. 123-163.

Butts, Charles, 1917, Mississippian formations of western Kentucky: Descriptions and correlations of the Mississippian formations of western Kentucky: Kentucky Geological Survey, ser. 4, v. 5, pt. 1, 119 p.

Cumings, E. R., 1922, Nomenclature and description of the geological formations of Indiana, in Logan, W. N., Cumings, E. R., Malott, C. A., Visher, S. S., Tucker, W. M., Reeves, J. R., and Legge, H. W., Handbook of Indiana geology: Indiana Department of Conservation Publications 21, pt. 4, p. 403-570.

Gray, H. H., 1970, Sample Formation, in Shaver, R. H., Burger, A. M., Gates, G. R., Gray, H. H., Hutchison, H. C., Keller, S. J., Patton, J. B., Rexroad, C. B., Smith, N. M., Wayne, W. J., and Wier, C. E., Compendium of rock-unit stratigraphy in Indiana: Indiana Geological Survey Bulletin 43, p. 159-160.

Gray, H. H., 1986, Sample Formation, 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. 136.

Gray, H. H., and Perry, T. G., 1956, Local lithologic discontinuities in Reelsville (lower Chester) Limestone of Indiana: American Association of Petroleum Geologists Bulletin, v. 40, p. 1,005-1,009.

Gray, H. H., Dawson, T. A., McGregor, D. J., Perry, T. G., and Wayne, W. J., 1957, Rocks associated with the Mississippian-Pennsylvanian unconformity in southwestern Indiana: Indiana Geological Survey Field Conference Guidebook 9, 42 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.

Malott, C. A., 1919, The "American Bottoms" region of eastern Greene County, Indiana–a type unit in southern Indiana physiography: Indiana University Studies, v. 6, no. 40, 61 p.

Malott, C. A., 1952, Stratigraphy of the Ste. Genevieve and Chester formations of southern Indiana: Ann Arbor, Michigan, Edwards Letter Shop, 105 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.

Sullivan, D. M., 1972, Subsurface stratigraphy of the West Baden Group in Indiana: Indiana Geological Survey Bulletin 47, 31 p.

Swann, D. H., 1963, Classification of Genevievian and Chesterian (Late Mississippian) rocks of Illinois: Illinois State Geological Survey Report of Investigations 216, 91 p.

Swann, D. H., and Atherton, Elwood, 1948, Subsurface correlations of lower Chester strata of the Eastern Interior Basin: Journal of Geology, v. 56, p. 269-287.

For additional information contact:

Nancy Hasenmueller (
Date last revised: April 6, 2017