Men are shown working a lead mine in the Upper Mississippi Valley. The operators of the lift stand above layers of soil, then limestone, then the layer being mined, in which the lighter-shaded rock is the lead ore. The drawing appears in
David Dale Owen, Report of a Geological Exploration of Part of Iowa, Wisconsin, and Illinois, Made under Instructions from the Secretary of the Treasury...in the...Year 1839, reprinted with illustrations in Senate Documents, 28 Congress, 1 session, 4: part 2, no. 408, dated 1844.
