XV. The Peorian Interglacial Stage.

This is the interglacial interval between the Iowan glacial and the Wisconsin. It was probably not of long continuance and is chiefly remarkable for the deposition of loess. This has not furnished any important collections of vertebrate fossils. The type locality for the Peorian stage is a locality east of Peoria, Illinois. Leverett (Monogr. XXXVIII, U. S. Geol. Surv.) mentions several cases in which old soils believed to belong to the Peorian were observed in Illinois. None of these has furnished vertebrate fossils. It is usually difficult to distinguish the Sangamon from the Peorian soils.