Old Port Formation

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Old Port Formation
Stratigraphic range: Early Devonian
Ridgeley SS Warrior Ridge.jpg
Ridgeley Member of the Old Port Formation
Type sedimentary
Unit of Helderberg Group
Sub-units Ridgeley, Shriver, Mandata, Corriganville, and New Creek Members
Underlies Onondaga Formation
Overlies Keyser Formation
Thickness 150 to 190 ft (Mifflintown Quadrangle in PA)[1]
Primary limestone, sandstone
Other chert, shale
Region Appalachian Mountains
Extent Pennsylvania, Maryland, Virginia, West Virginia
Type section
Named by Conlin and Hoskins, 1962[1]

The Devonian Old Port Formation is a mapped bedrock unit in Pennsylvania, Maryland, and West Virginia, USA. Members of the unit are also mapped in New Jersey and Virginia as parts of other formations or groups. Current usage by U.S. Geological Survey (USGS), however, restricts the name Old Port Formation to Pennsylvania.[2]


The Old Port Formation consists of several members with varying lithologies, which are (in ascending stratigraphic order): New Creek Member (limestone), Corriganville Member (limestone), Mandata Member (shale), Shriver Member (cherty limestone), and Ridgeley Member (sandstone). Where the Shriver Chert does not occur it may be replaced by the Licking Creek Limestone.[3] It was originally combined from the Helderberg Group and Oriskany Group by Conlin and Hoskins in 1962 to form a single Formation with the above members.[1]

Ridgeley Member[edit]

The Ridgeley Member was first described as a member of the Oriskany Formation by Swartz and others (1913), as a calcareous sandstone which passes into an arenaceous limestone.[4] It is still mapped as part of the Oriskany Group in New Jersey.[5]

The type locality is at the town of Ridgeley, Mineral County, West Virginia.[4]

The sandstone of the Ridgeley Member has been extensively mined due to its very pure quartz suitable for glass. The glass derived from the sandstone was used for lenses on the Hubble Space Telescope.[6]

A separate formation, the Oriskany Sandstone, is a lateral equivalent of the Ridgeley Member, but bounded above and below by unconformities.

A panorama of a roadcut through the Ridgeley Member along U.S. Route 522 north of Shirleysburg, Huntingdon County, Pennsylvania, April 2011

Shriver Member[edit]

The Shriver Member, or Shriver Chert, was first described as a member of the Oriskany Formation by Swartz and others (1913), as dark siliceous shale with much black impure chert in nodules or layers of nodules.[4] It is named after Shriver Ridge (the type locality), Allegany County, Maryland, and was originally mapped as the basal unit of the Oriskany Formation.

In Maryland and West Virginia, the Shriver is mapped as part of the Helderberg Group.[7]

In central Pennsylvania it is mapped as part of the Old Port Formation.[8]

In New Jersey it is mapped as the middle unit of the Oriskany Group.[5]

Mandata Member[edit]

The Mandata Shale of the Helderberg Group was first introduced by F. M. Swartz in 1938,[9] mainly with reference to the overlying Licking Creek Limestone. The type locality is about 0.25 miles south of Mandata, Pennsylvania, on Route 225.

Corriganville Member[edit]

The Corriganville Limestone was first described by J. W. Head in 1972 as part of the Helderberg Group in Allegany County, Maryland, as a gray limestone with chert.[10] C. R. Wood first mapped it as part of the Old Port Formation in Pennsylvania.[11]

The type locality is a railroad cut 0.3 mi southeast of Corriganville, Alleghany County, Maryland.[10]

A panorama of outcrop of Keyser Formation (left) and Corriganville and New Creek Members in Everett, Pennsylvania along Business Route 30 (West Main Street), facing north, April 2011

New Creek Member[edit]

The New Creek Member was first described by Bowen only as a limestone that is replaced by the Elbow Ridge Sandstone near Hancock, Maryland.[12] Bowen later described it as a massive limestone overlying the Keyser Formation.[13] C. R. Wood first mapped it as part of the Old Port Formation in Pennsylvania.[11]

Licking Creek Member[edit]

The Licking Creek Limestone of the Helderberg Group was first introduced by F. M. Swartz in 1938,[9] and was described more fully in 1939.[14] The unit consists of layers and nodules of black chert interbedded with light-gray crystalline limestone. The type locality is a bluff on the south side of Licking Creek, about one mile east of Warren Point, Franklin County, Pennsylvania.


Brachiopods are occasionally abundant (as casts) in the Ridgeley Member.

The brachiopods Costispirifer arenosus, Beachia immatura, Leptocoelia flabellites, Metaplasia paucicostata, Plicoplasia tribuarius, and Chonetes hudsonicus are present in the Shriver Member around the type locality of Shriver Ridge.[4] Ostracods are also present in the Shriver Member.[15][16]

The Old Port Formation contains conodonts.[17]

Notable Exposures[edit]

  • Old quarry in Tyrone, Pennsylvania, west of Sink Run and along U.S. Route 22[18]
  • Two exposures in Everett, Pennsylvania:
    • U.S. Route 30 (Everett Bypass) roadcut through Warrior Ridge north of Everett
    • Another exposure along business Route 30 on the west side of Everett (pictured above)
  • The Sinnett-Thorn Mountain Cave System is developed in the Keyser Formation and overlying New Creek and Corriganville Limestone Members[19]

See also type localities listed in subsections above.


Relative age dating of the Old Port places it in the Lower Devonian period. It rests conformably atop the Keyser Formation and usually unconformably below the Needmore Formation[20] or below the Onondaga Formation.

Economic Uses[edit]

The Ridgeley Member is mined extensively in Pennsylvania and Maryland.


  1. ^ a b c Conlin, R.R., and Hoskins, D.M., 1962, Geology and mineral resources of the Mifflintown quadrangle, Pennsylvania: Pennsylvania Geological Survey Topographic and Geologic Atlas, 4th series, 126, 46 p., scale 1:24,000
  2. ^ https://ngmdb.usgs.gov/Geolex/Units/OldPort_3095.html
  3. ^ Geologic Map of Pennsylvania, Berg, T. M., Edmunds, W. E., Geyer, A. R., and others, compilers, 1980, Pennsylvania Geological Survey, 4th ser., Map 1, scale 1:250,000 [1]
  4. ^ a b c d Swartz, C.K., Rowe, R.B., Schuchert, Charles, and Maynard, T.P., 1913, Lower Devonian in Maryland; Local sections of the Lower Devonian [of Maryland]; Correlation of the Lower Devonian, IN Swartz, C.K., and others, Lower Devonian, text: Maryland Geological Survey Systematic Report, p. 23-66, 96-190.
  5. ^ a b Monteverde, D.H., 1992, Bedrock geologic map of the Sussex County, New Jersey, portions of the Culvers Gap and Lake Maskenozha quadrangles: New Jersey Geological Survey Geologic Map, 92-1, 1 sheet, scale 1:24,000
  6. ^ Abplanalp, J. and Lehmann, D., Juniata College, Huntingdon, PA: High Resolution Stratigraphy and Parasequences of the Oriskany Sandstone, Mapleton, Pennsylvania [2]
  7. ^ Dennison, J.M., 1963, Geology of the Keyser quadrangle, West Virginia-Maryland: West Virginia Geological and Economic Survey Geologic Map, GM-1, 1 sheet, scale 1:24,000
  8. ^ Hoskins, D.M., 1976, Geology and mineral resources of the Millersburg 15-minute quadrangle, Dauphin, Juniata, Northumberland, Perry, and Snyder Counties, Pennsylvania: Pennsylvania Geological Survey Topographic and Geologic Atlas, 4th series, 146, 38 p., scale 1:24,000
  9. ^ a b Swartz, F.M., 1938, (Abstract) GSA Bulletin, v. 49, no. 12, pt. 2, p. 1923
  10. ^ a b Head, J.W., III, 1972, Upper Silurian-Lower Devonian stratigraphy and nomenclature in the central Appalachians, IN Guidebook for the 37th annual field conference of Pennsylvania geologists: Field Conference of Pennsylvania Geologists, no. 37, p. 96-103.
  11. ^ a b Wood, C.R., 1980, Summary groundwater resources of Centre County, Pennsylvania: Pennsylvania Geological Survey Water Resource Report, 4th series, no. 48, 60 p.
  12. ^ Bowen, Z.P., 1966, Brachiopods and stratigraphy of the Elbow Ridge Sandstone (Lower Devonian) of Pennsylvania, Maryland, and West Virginia: Journal of Paleontology, v. 40, no. 5, p. 1051-1062.
  13. ^ Bowen, Z.P., 1967, Brachiopods of the Keyser Limestone (Silurian-Devonian) of Maryland and adjacent areas: Geological Society of America Memoir, 102, 103 p.
  14. ^ Swartz, F.M., 1939, The Keyser limestone and Helderberg group, IN Willard, Bradford, Swartz, F.M., and Cleaves, A.B., The Devonian of Pennsylvania: Pennsylvania Geological Survey General Geology Report, 4th series, no. 19-G, p. 29-91.
  15. ^ Swartz, F. M., 1932, Revision of the Ostracode Family Thlipsuridae, with Descriptions of New Species from the Lower Devonian of Pennsylvania. Journal of Paleontology, Vol. 6, No. 1, Mar. 1932, pp. 36-58 [3]
  16. ^ Swartz, F. M., 1936, Revision of the Primitiidae and Beyrichiidae, with New Ostracoda from the Lower Devonian of Pennsylvania. Journal of Paleontology, Vol. 10, No. 7, Oct. 1936, pp. 541-586 [4]
  17. ^ Harris, A.G., Stamm, N.R., Weary, D.J., Repetski, J.E., Stamm, R.G., and Parker, R.A., 1994, Conodont color alteration index (CAI) map and conodont-based age determinations for the Winchester 30' x 60' quadrangle and adjacent area, Virginia, West Virginia, and Maryland: U.S. Geological Survey Miscellaneous Field Studies Map, MF-2239, 40 p., 1 sheet, scale 1:100,000
  18. ^ Faill, R.T., Glover, A.D., and Way, J.H., 1989, Geology and mineral resources of the Blandburg, Tipton, Altoona, and Bellwood quadrangles, Blair, Cambria, Clearfield and Centre Counties, Pennsylvania: Pennsylvania Geological Survey Topographic and Geologic Atlas, 4th series, 86, 209 p., scale 1:24,000 and 1:48,000
  20. ^ Stratigraphic correlation chart of Pennsylvania, T. M. Berg, M. K. McInerney, J. H. Way, and D. B. MacLachlan. 1983; 3rd printing, revised, 1993. 1 sheet, 42" x 58", plus 2 p. addendum.

See also[edit]