Along the Raccoon River in Polk County, along the Des Moines river, and along the tributaries of the Des Moines, from Warren County there is a terrace, previously noted by geological workers. An important question with the writer has been this: Do the gravels in this terrace form one continuous deposit, or do they form two separate deposits, an upper of Wisconsin or post-Wisconsin age, and an underlying portion that is older than the upper deposit, and possibly of Aftonian age? This question was suggested by a division in the sand recorded in well records, and by the presence of fossils of large mammals that had been found at a depth of perhaps twenty-five feet below the surface of the sand. The identification of these fossils in the spring of 1914 by Professor Oliver P. Hay of the United States National Museum, and the publication of topographic maps of regions along the Des Moines River, make a review of local evidence seem desirable.
Proceedings of the Iowa Academy of Science
©1915 Iowa Academy of Science, Inc.
Tilton, John L.
"The Age of the Terrace South of Des Moines, Iowa,"
Proceedings of the Iowa Academy of Science, 22(1), 233-236.
Available at: https://scholarworks.uni.edu/pias/vol22/iss1/29