Silurian - Ordovician Vassalboro formation (MESOv;0)

State	Maine
Name	Silurian - Ordovician Vassalboro formation
Geologic age	Silurian - Ordovician
Original map label	SOv
Comments	The Vassalboro formation is typically a massive, bluish-gray sandstone. Locally it is quartzite; shaly layers have been altered to pyritiferous mica schists. Contains numerous calcareous beds. Increase in the intensity of metamorphism of the Vassalboro formation produced the lime-silicate gneiss of the Androscoggin formation. The Androscoggin of the Tacoma Lakes area was identified by Perkins and Smith (1925) as the Vassalboro. Due to its varying lithologies, the Vassalboro is revised to the Vassalboro formation. (ME061). Unit description from USGS GEOLEX website (ME078). GS - Greenschist facies E - Epidote-amphibolite facies AA - Low rank amphibolite facies AB - Medium rank amphibolite facies AC - High rank amphibolite facies Protolith M - Calcareous sandstone; interbedded sandstone and impure limestone
Primary rock type	sandstone
Secondary rock type	quartzite
Other rock types	schist; limestone
Lithologic constituents	Major Sedimentary > Clastic > Sandstone (Calcareous)GS - Greenschist facies E - Epidote-amphibolite facies AA - Low rank amphibolite facies AB - Medium rank amphibolite facies AC - High rank amphibolite facies Protolith M - Calcareous sandstone; interbedded sandstone and impure limestone Minor Sedimentary > Carbonate > Limestone (Calcareous)GS - Greenschist facies E - Epidote-amphibolite facies AA - Low rank amphibolite facies AB - Medium rank amphibolite facies AC - High rank amphibolite facies Protolith M - Calcareous sandstone; interbedded sandstone and impure limestone Incidental Metamorphic > Schist (Calcareous)GS - Greenschist facies E - Epidote-amphibolite facies AA - Low rank amphibolite facies AB - Medium rank amphibolite facies AC - High rank amphibolite facies Protolith M - Calcareous sandstone; interbedded sandstone and impure limestone Metamorphic > Metasedimentary > Metaclastic > Quartzite (Calcareous)GS - Greenschist facies E - Epidote-amphibolite facies AA - Low rank amphibolite facies AB - Medium rank amphibolite facies AC - High rank amphibolite facies Protolith M - Calcareous sandstone; interbedded sandstone and impure limestone
Map references	Digital bedrock data downloaded from Maine Office of GIS in September 2005 from http://apollo.ogis.state.me.us/catalog/catalog.asp?state=2&extent=cover#bedrock Bedrock units table (publication date 11/15/2002) downloaded from same site. Permission to redistribute these data granted by Dr. Robert Marvinney, State Geologist of Maine, in September 2006. [http://apollo.ogis.state.me.us/catalog/catalog.asp?state=2&extent=cover#bedrock]
Unit 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. Pankiwskyj, K.A., Ludman, A., Griffin, J.R., and Berry, W.B.N., 1976, Stratigraphic relationships on the southeast limb of the Merrimack synclinorium in central and eastern Maine: Geol. Soc. Amer., Memoir 146, p. 263-280. Fisher, L.W., 1941, Structure and metamorphism of Lewiston, Maine, region: Geological Society of America Bulletin, v. 52, no. 1, p. 107-160. USGS Geologic Names Lexicon (GEOLEX) [http://ngmdb.usgs.gov/Geolex/]
Geographic coverage	Androscoggin - Cumberland - Hancock - Kennebec - Lincoln - Penobscot - Sagadahoc - Somerset - Waldo - Washington - York