Devonian Hedgehog Formation (MEDhd;0)

State	Maine
Name	Devonian Hedgehog Formation
Geologic age	Devonian
Lithologic constituents	Major Igneous > Volcanic > Felsic-volcanicW - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite; Protolith W - Mafic to felsic volcanic rocks Igneous > Volcanic > Mafic-volcanicW - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite; Protolith W - Mafic to felsic volcanic rocks
Comments	Named as a formation for Hobbstown Township in northeast part of Spencer Lake 15-min quad, northern Somerset Co., ME. Type area is Hobbstown Township between Hardwood and Spencer Mountains. Main part consists of interbedded coarse-grained arkose and conglomerate with poorly rounded pebbles and cobbles, all blue gray, gray, dark green, and white weathering. Arkose is fine to coarse quartz grains with 10 to 30 percent feldspar. Conglomerate is felsite, platy calcareous siltstone, and limestone cobbles. Thickness is up to 1,500 ft. Overlies Hardwood Mountain formation in some places and basement complex in others. Lower conglomerate member consists of felsite and granitic pebbles ranging from fraction of an inch to several feet in diameter. Matrix is medium-grained, quartzitic, dark sandstone. Thickness is up to 200 ft. Unconformably overlies Hardwood Mountain formation. Member is absent outside of Hobbstown type area. Report includes geologic map and correlation chart. Overall age is Late Silurian to Early Devonian. Late Silurian fossils occur in a thin bed above base of lower member, but they may have been reworked from Hardwood Mountain formation. Member is at least of Tonoloway (Late Silurian) age but may be as young as lower part of Seboomook formation of New Scotland to Oriskany (Early Devonian) age. Ostracodes in lower member correlate with those in Hardwood Mountain formation. Brachiopods similar to Henryhouse and Brownsport formations (TN and OK). (ME003). Unit description from USGS GEOLEX website (ME078). GS - Greenschist facies; Protolith H - Lithic sandstone and conglomerate.
Stratigraphic units	Dockendorff Group
References	Osberg, P.H., Hussey, A.M., and Boone, G.M., 1985, Bedrock geologic map of Maine: Maine Geological Survey, Dept. of Conserv., scale 1:500,000.
NGMDB product	NGMDB product page for 16547
Counties	Aroostook

State

Name

Devonian Hedgehog Formation

Geologic age

Devonian

Lithologic constituents

Major

Igneous > Volcanic > Felsic-volcanicW - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite; Protolith W - Mafic to felsic volcanic rocks

Igneous > Volcanic > Mafic-volcanicW - Weakly metamorphosed; contains local occurrences of prehnite and pumpellyite; Protolith W - Mafic to felsic volcanic rocks

Comments

Named as a formation for Hobbstown Township in northeast part of Spencer Lake 15-min quad, northern Somerset Co., ME. Type area is Hobbstown Township between Hardwood and Spencer Mountains. Main part consists of interbedded coarse-grained arkose and conglomerate with poorly rounded pebbles and cobbles, all blue gray, gray, dark green, and white weathering. Arkose is fine to coarse quartz grains with 10 to 30 percent feldspar. Conglomerate is felsite, platy calcareous siltstone, and limestone cobbles. Thickness is up to 1,500 ft. Overlies Hardwood Mountain formation in some places and basement complex in others. Lower conglomerate member consists of felsite and granitic pebbles ranging from fraction of an inch to several feet in diameter. Matrix is medium-grained, quartzitic, dark sandstone. Thickness is up to 200 ft. Unconformably overlies Hardwood Mountain formation. Member is absent outside of Hobbstown type area. Report includes geologic map and correlation chart. Overall age is Late Silurian to Early Devonian. Late Silurian fossils occur in a thin bed above base of lower member, but they may have been reworked from Hardwood Mountain formation. Member is at least of Tonoloway (Late Silurian) age but may be as young as lower part of Seboomook formation of New Scotland to Oriskany (Early Devonian) age. Ostracodes in lower member correlate with those in Hardwood Mountain formation. Brachiopods similar to Henryhouse and Brownsport formations (TN and OK). (ME003). Unit description from USGS GEOLEX website (ME078). GS - Greenschist facies; Protolith H - Lithic sandstone and conglomerate.

Stratigraphic units

Dockendorff Group

References

Osberg, P.H., Hussey, A.M., and Boone, G.M., 1985, Bedrock geologic map of Maine: Maine Geological Survey, Dept. of Conserv., scale 1:500,000.

NGMDB product

NGMDB product page for 16547

Counties

Aroostook