The Silurian strata of central Pennsylvania are excellently exposed along State Highway 22, on the north side of the Juniata River, opposite Mount Union, Pennsylvania. Good exposures of parts of the system can also be seen at several localities near Lewistown, 23 miles to the northeast. These combined sections display an almost complete 3000-foot sequence of Silurian deposits in the area and exhibit a number of diagnostic zones of ostracodes and other fossils. From Mount Union to Lewistown several of the formations undergo important lateral variations that are symptomatic of major changes occurring between western Maryland and eastern Pennsylvania. These two sections, accordingly, provide an excellent basis for study of the Silurian rocks of the region, and their accessibility gives them added value for the visiting geologist. Furthermore, they lie between the studied sections of western New York and of western Maryland and present additional data bearing on the . . .