Throughout most of northern Illinois and northeastern Iowa, the Maquoketa Group (upper Ordovician) is overlain unconformably by lower Silurian dolomitic strata. For the most part, this unconformity is clear cut and separates the blue-gray dolomitic shale of the Maquoketa from the dolostones of the Edgewood Formation or, in places where the Edgewood is absent, the Kankakee Limestone. However, at Bellevue, Iowa, along the bluffs of the Mississippi River, an unconformity, if present, is difficult to demonstrate. About 25 feet of blue-gray dolomitic shale that has blocky fracture and is interbedded with yellow-brown silty dolostone is difficult to assign to either the Maquoketa or the Edgewood (Scobey, 1938, p. 214). The small collection of graptolites discussed in this paper was obtained from the lower part of these transitional beds.