The attention of the writer was drawn to the nature and form of the buried pre-Cambrian basement of Wisconsin when he began the study and collection of well records for the Wisconsin Geological and Natural History Survey in 1912. The present study of this problem is by no means the first, for in 1869 I. A. Lapham2 published a map of Wisconsin on which he drew 100-foot contours on the base of the Paleozoic sediments. In 1915 Weidman 3 drew a generalized map of the top of the concealed pre-Cambrian with 250-foot contours. This map omitted all local irregularities. In the following year Jay,4 working under the direction of Lawrence Martin, mapped small areas near Baraboo. In 1925 Du Rietz5 published a small-scale contour map of the surface of the pre-Cambrian of North America.
The pre-Cambrian rocks of Wisconsin form an elongated geanticline which strikes approximately . . .