“With the rapid progress of detailed geologic investigation through‐out the world and the shift in viewpoint as one phase or another of the complex subject is emphasized, changes in classification must necessarily be made as rapidly as enough evidence is presented to convince the majority of geologists that they are desirable.”— Stanton.

“But while we can not now, and probably may never, hope to divide geologic time into centuries and milleniums, we can divide it into periods, each of which has its own special significance in the history of the earth.”— Grabau.

This paper has as its subject “Classification and Duration of the Pleistocene Period.” Its chief purpose is to trace briefly the history of development of the present classification of the Pleistocene, to suggest a revision of this classification, and to present an estimate of the duration of each of the glacial and interglacial ages of the Pleistocene, . . .

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