Drilling data in the Montfort, Rewey, Mifflin, Belmont, and Calamine quadrangles, Wisconsin

Sixty-six churn drill holes aggregating 10,351 feet were drilled in the fall of 1955 in the zinc-lead district of southwestern Wisconsin (fig. 1). This drilling was part of a cooperative program of geologic mapping by the U. S. Geological Survey and the Wisconsin Geologic and Natural History Survey.

The holes penetrate the Maquoketa, Galena, Decorah, and Platteville formations of Late and Middle Ordovician age in areas of sparse outcrop and subsurface information. They provide basic data for stratigraphic study and for the projection of geologic structures in these areas. Exact location of the holes is shown in figs. 2, 3, 4, 5, and 6.

Generalized descriptive logs of the 66 holes were prepared mainly from driller's logs, and from a field study of the drill cuttings by J. E. Carlson. Where delineation of the formations drilled was difficult in the field, the cuttings were examined by binocular microscope.