In 1893 James D. Dana remarked that the concept of multiple glaciation had been advanced by midwestern geologists, while geologists who had done most of their fieldwork in the Northeast advocated a unified glacial period. Midwestern geologists interpreted the lobate terminal moraine ranging across much of the United States from Long Island to the Rockies as the boundary of the most recent ice sheet, and more southerly extramorainal drift as evidence of at least one earlier ice incursion, separated in time by a substantial, warmer interglacial interval or intervals, from the ice sheet that had deposited the terminal moraine. Geologists working east of Ohio, where the discrepancy between the terminal moraine and the extramorainal drift was less marked, tended to see the advance and retreat of the ice sheet as a single event, with minor oscillation and pauses of the ice front. The chief disputants in this debate were T. C. Chamberlin, professor of geology at the University of Chicago and head of the USGS Pleistocene Division, and G. Frederick Wright, former field geologist with the USGS and professor of theology at Oberlin College, but other prominent American geologists including Dana, W J McGee, R. D. Salisbury, Warren Upham, and Frank Leverett also took part. The debate was greatly enlivened by underlying motives much more complex than the midwestern versus northeastern division suggested by Dana. Among these less objective factors were personal animosities, Chamberlin's patronal attitude toward science and its presentation to the public, Wright's introduction of man into the North American Pleistocene, and resentment of a perceived arrogance on the part of government science.

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