The Galena Group or Galena Limestone refers to a sedimentary sequence of

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

that was deposited atop the Decorah Shale. It is part of the Ordovician stratigraphy of the Upper Midwestern United States. It was deposited in a calm marine environment, and is fossiliferous.Mossler, J. and Benson, S., 1995, 1999, 2006
Fossil Collecting in the Twin Cities Area
Minnesota at a Glance: Minnesota Geological Survey: University of Minnesota.

References

Geologic groups of Minnesota Ordovician Minnesota Limestone groups of the United States {{US-geologic-formation-stub