CINCINNATIAN SERIES

uppermost rocks of the Ordovician System, defined on the basis of exposures seen around the region of Cincinnati, Ohio, where they consist of numerous limestone formations that are richly fossiliferous. (The Ordovician Period lasted from 505 to 438 million years ago.) To the south and west of Cincinnati, the deposits are fragmentary, whereas deposits found in the Appalachian region are thick and consist of sandstones, shales, and conglomerates. The shaly limestones of the type area have long attracted students of ancient animal life; specimens, excellently preserved, often are weathered free of their matrix. A number of great American paleontologists began as amateur collectors of Cincinnatian fossils in Ohio.