U.S. Geological Survey Home AASG Logo USGS HOME CONTACT USGS SEARCH USGS
National Geologic Map Database
Geologic Unit: Milroy
Search archives
Map showing publication footprint
  • Usage in publication:
    • Milroy limestone [unranked]
  • Modifications:
    • Original reference
  • Dominant lithology:
    • Limestone
    • Dolomite
  • AAPG geologic province:
    • Appalachian basin
Publication:

Swartz, F.M., Rones, Morris, Donaldson, A.C., and Hea, J.P., 1955, Stratigraphy of Ordovician limestones and dolomites of Nittany Valley in area from Bellefonte to Pleasant Gap, Pennsylvania; Trip 1(F), IN Guidebook for the 21st annual field conference of Pennsylvania geologists: Field Conference of Pennsylvania Geologists, no. 21, p. 1-25.


Summary:

Pg. F5, F6, F14, F15 (geol. map). Milroy limestone [unranked] in Loysburg limestone. Name Milroy is proposed by Rones for the "tiger-striped" beds of Kay's reports [see G.M. Kay, 1944, Jour. Geol., v. 52, no. 1], in which dolomitic bands of irregular 1- to 2-inch interlayers of dolomitic limestone and purer limestone weather with distinct relief on many of the exposed surfaces that transect the bedding of the rock. Thickness 300 feet. Underlies Clover limestone [unranked] in Loysburg limestone. Overlies Tea Creek dolomite (new) of Bellefonte group. Chazyan stage.
[Type area]: Bellefonte to Pleasant Gap, Nittany Valley, Centre Co., central PA. [Probably named from town of Milroy, north of Reedsville, Armagh Twp., Lewistown 15-min quadrangle, Mifflin Co., central PA.]
[Typographical error (US geologic names lexicon, USGS Bull. 1350, p. 491): The Milroy lies within the Loysburg limestone, not beneath it.]

Source: Publication; US geologic names lexicon (USGS Bull. 1350, p. 491).


Map showing publication footprint
  • Usage in publication:
    • Milroy Member
  • Modifications:
    • Revised
  • AAPG geologic province:
    • Appalachian basin
Publication:

Chafetz, H.S., 1969, Carbonates of the Lower and Middle Ordovician in central Pennsylvania: Pennsylvania Geological Survey General Geology Report, 4th series, no. 58, 39 p.


Summary:

Revised the Milroy to the Milroy Member of the Loysburg Formation in central PA. Unit is lowest member of formation. Occurs as lens-shaped masses ranging from 0 to 400 feet thick. Consists of interbedded limestone and dolomite. The lower contact is placed beneath the first occurrence of limestone and above the highest dolomite of the underlying Tea Creek Member of the Bellefonte Formation. The upper contact is placed beneath the lowest bed with abundant and diverse fauna above which no dolomite beds occur that are greater than 3 feet thick. Underlies the Clover Member of the Loysburg.

Source: GNU records (USGS DDS-6; Reston GNULEX).


Map showing publication footprint
  • Usage in publication:
    • Milroy Member
  • Modifications:
    • Revised
  • AAPG geologic province:
    • Appalachian basin
Publication:

Rones, Morris, 1969, A lithostratigraphic, petrographic, and chemical investigation of the lower Middle Ordovician carbonate rocks in central Pennsylvania: Pennsylvania Geological Survey General Geology Report, 4th series, no. 53, 224 p.


Summary:

Used Milroy Limestone of the Loysburg Group in place of "Tiger-striped" member of Kay (1944). Lowest unit of Loysburg. Consists of medium dark-gray, coarse calcilutite with numerous 1-inch light-gray weathering dolomitic bands that stand out in relief. Thickness is about 410 feet. Unconformably(?) overlies Bellefonte Formation of Beekmantown Group and underlies the Clover Limestone. The Milroy is of Middle Ordovician age.

Source: GNU records (USGS DDS-6; Reston GNULEX).


Map showing publication footprint
  • Usage in publication:
    • Milroy Member
  • Modifications:
    • Overview
  • AAPG geologic province:
    • Appalachian basin
Publication:

Berg, T.M. (compiler), 1980, Geologic map of Pennsylvania: Pennsylvania Geological Survey State Map, 4th series, 1, scale 1:250,000


Summary:

The Milroy Member of the Loysburg Formation in central PA consists of alternating laminated limestone, dolomitic limestone, and dolomite. Overlies the Bellefonte Formation and underlies Clover Member of Loysburg.

Source: GNU records (USGS DDS-6; Reston GNULEX).


Search archives

For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.

Asterisk (*) indicates usage by the U.S. Geological Survey. Other usages by state geological surveys.

"No current usage" (†) implies that a name has been abandoned or has fallen into disuse. Former usage and, if known, replacement name given in parentheses ( ).

Slash (/) indicates name does not conform with nomenclatural guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005). This may be explained within brackets ([ ]).