As most are aware, there are areas of drift external to any terminal moraines, the origin of which is still in dispute. On general principles, it would be expected that numerous lakes would have frequently occurred during the Ice Age. As the ice advanced, streams would frequently be dammed, and their channels more or less changed, and the might of the ice, with its chilling effect, in level areas would not infrequently produce a subsidence toward the ice, which would often become filled with the floods escaping from the ice.
Proceedings of the Iowa Academy of Sciences
©1890 Iowa Academy of Science, Inc.
Todd, J. E.
"The Shore-Lines of Ancient Glacial Lakes,"
Proceedings of the Iowa Academy of Science, 1(Pt. 2), 17-19.
Available at: https://scholarworks.uni.edu/pias/vol1/iss2/7