|Paleozoic Stratigraphy of the Upper Midwest, USA
Dates are approximate, and deposition occurred at slightly different times in different areas
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.
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