Work was begun on the deep well in October, 1892, but it was not completed until the following year. The ordinary churn drill was used and the hole was first drilled eight inches in diameter, but later the upper portion was enlarged to ten inches. The record has been more carefully kept than is usual in drilling such wells, but cannot be relied upon as absolutely exact. In many cases the fragments of the overlying stratum are mixed with that underneath, and the thickness of each formation cannot be exactly determined. This renders the results only approximately correct, but it is believed that a fair degree of accuracy has been attained.
Proceedings of the Iowa Academy of Sciences
©1894 Iowa Academy of Science, Inc.
Jones, Arthur J.
"Record of the Grinnell Deep Boring,"
Proceedings of the Iowa Academy of Science, 2(1), 31-35.
Available at: https://scholarworks.uni.edu/pias/vol2/iss1/10