Iowa has been repeatedly and so thoroughly planed off and worked over by continental glaciers of no less than five great ice-invasions that it could be hardly expected that any remnants of the softer pre-glacial formations, if there ever were any deposited within the state's boundaries, would survive. Moreover, the state is now everywhere so deeply covered by the several till-sheets and the vast eolian soil-mantles as to effectually conceal all traces of the existence of pre-glacial deposits which we ordinarily refer to the Tertiaries.
Proceedings of the Iowa Academy of Science
©1913 Iowa Academy of Science, Inc.
"Recognition of Beds of Tertiaric Age in Our state,"
Proceedings of the Iowa Academy of Science, 20(1), 202-202.
Available at: https://scholarworks.uni.edu/pias/vol20/iss1/19