This paper treated particularly of the morainic till of the Missouri Valley. To explain the origin of this till, there are two theories acceptable: one that it is sub-glacial, the other, that it was formed at the bottom of a glacial lake, gradually filling with debris brought from a glacier and the shore, by ice-rafts.
Proceedings of the Iowa Academy of Sciences
©1887 Iowa Academy of Science, Inc.
Todd, J. E.
"The Origin of the Extra-Morainic Till,"
Proceedings of the Iowa Academy of Science, 1(Pt. 1), 12-14.
Available at: https://scholarworks.uni.edu/pias/vol1/iss1/10