Of all geological phenomena represented in Iowa those illustrating volcanic action are the rarest. Although we already know of the presence of very ancient lava-flows, which are disclosed in deep-well drillings, these are associated with rocks very much older than any outcropping in the state. These are the Keewenawan porphyries of the Northwest. From that very ancient date to the present there is not the slightest sign of volcanic activity discernible in all our very full geologic record. The finding, a short time ago, in the city of Des Moines, of very considerable beds of typical volcanic ash is therefore a circumstance of more than passing interest.
Proceedings of the Iowa Academy of Science
©1921 Iowa Academy of Science, Inc.
"Discovery of Volcanic Ash in Iowa,"
Proceedings of the Iowa Academy of Science, 28(1), 49-53.
Available at: https://scholarworks.uni.edu/pias/vol28/iss1/9