John C. Frye and H. B. Willman
The Quaternary System was proposed in 1829 by Desnoyers (Wilmarth, 1925, p. 43), who recognized it as a unit distinct from the Tertiary System. Its definition depends on the placement of the end of Tertiary time. The Pleistocene Series also began at that time, and in Illinois classification the Quaternary System is equivalent to that one series. In 1925 the Pleistocene was classified as a system in Illinois, and the term "Quaternary" was not used until 1950 when the Pleistocene was reduced to a series and the Quaternary reinstated as a system. The Quaternary System includes the rocks being deposited at present.
WILMARTH, M. G., 1925, Geologic time classification of the United States Geological Survey compared with other classifications: United States Geological Survey Bulletin 769, 138 p.
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