For convenience the flint beds of the Burlington limestones are usually separated into two divisions, known as the "lower" and '' upper '' flint beds. The lower series is probably from fifteen to twenty feet thick and the upper a little more. They have always been classed as the latest deposits of the Lower Burlington and Upper Burlington limestones, respectively. The lower beds are not so continuously chert as the Upper; in fact much of the deposit is siliceous shale mixed with clay and containing thin bands of limestone. There are also certain strata which look like heavy-bedded limestone, but which contain so much siliceous and argillaceous matter as to be utterly worthless. As already stated the upper series is somewhat the thicker. There is also a much greater proportion of chert and much less siliceous shale, while the amount of limestone remains about the same.
Proceedings of the Iowa Academy of Sciences
©1894 Iowa Academy of Science, Inc.
Fultz, Francis M.
"Formation of the Flint Beds of the Burlington Limestones,"
Proceedings of the Iowa Academy of Science, 2(1), 177-177.
Available at: https://scholarworks.uni.edu/pias/vol2/iss1/38