Attention is directed to the value of volcanic ash-beds intercalated in other strata as indices to precise correlation of geological terranes. Such ash-beds, when once recognized, are often found to be wide-spread ; and being formed under conditions independent of water-laid basinal deposits pass uninterruptedly from one province to another. At present the most important clue to an horizon of this kind to be looked for in Iowa is an Ordovicic one near the base of the Decorah shales.
Proceedings of the Iowa Academy of Science
©1925 Iowa Academy of Science, Inc.
"New Method of Precise Geological Correlation,"
Proceedings of the Iowa Academy of Science, 32(1), 362-362.
Available at: https://scholarworks.uni.edu/pias/vol32/iss1/69