Many of the photographs used in these articles are also in the Samuel Calvin Photographs collection.
Current Volume: Volume 38 (1941)
Forty-ninth and Fiftieth Annual Reports of the State Geologist p. vii-xii
Arthur C. Trowbridge
The Illinoian and Post-Illinoian Pleistocene Geology of Iowa p. 1-262
George F. Kay and Jack B. Graham