Late Ordovician Graptolites from the Maquoketa Formation in Eastern Missouri

Climacograptus mississippiensis Ruedemann and Orthograptus truncatus var. socialis (Lapworth) are described from a higher and a lower stratigraphic interval respectively in the Maquoketa Formation at an exposure approximately 24 miles south of St. Louis, Missouri. The formation at the graptolite-bearing locality is 24.7 feet thick and is predominantly shale. The graptolites are indicative of a latest Ordovician (graptolite Zone 15) age and suggest that the Maquoketa Formation at this locality is correlative with the uppermost part of the Maquoketa Formation in Iowa and with the Richmond or upper part of the Maysville. The stratigraphic data and correlations indicate that the formation in eastern Missouri is thinner and more dominantly shale than it is either to the north or east.