In the Upper Mississippi Valley for a considerable period after the mines began to be operated much more lead than zinc was produced. It was not until 1860 that the latter metal came into market. Since then the zinc production has rapidly increased. During the ten years previous to 1882 the output of zinc more than doubled that of lead, while in 1889, according to the last federal census report the proportion between the two was as 18 to 1 for the entire region.
Proceedings of the Iowa Academy of Sciences
©1893 Iowa Academy of Science, Inc.
Leonard, A. G.
"Occurrence of Zinc in Northeastern Iowa,"
Proceedings of the Iowa Academy of Science, 1(Pt. 4), 48-52.
Available at: https://scholarworks.uni.edu/pias/vol1/iss4/18