Glenwood Shale

It lies under the Platteville Limestone and above the Saint Peter Sandstone.

Together, these three units represent a sequence of sea level rise during Ordovician time.

Because it is often very thin (~10 cm or less in the Twin Cities), it is often ignored in the general stratigraphy.

University of Minnesota: River Bluffs homepage Archived 2008-09-28 at the Wayback Machine

This article about a specific stratigraphic formation in the United States is a stub.

The Glenwood shale cropping out in Minneapolis , Minnesota . In this photo, it is the thin, darker layer that lies between the Platteville Limestone (above: the less-eroded, layered unit that constitutes the majority of the photo) and the St. Peter Sandstone (below: a thin, white stripe of in-place rock followed by a slope of eroded St. Peter Sandstone material).