Zinc and lead deposits of the Upper Mississippi Valley
The zinc and lead mines of the upper Mississippi Valley are in the southwest portion of Wisconsin and in adjacent parts of Illinois mid Iowa. The boundaries of the region are in part indefinite, since sporadic occurrences of the minerals are found outside the mining region proper. It is usual to define the area as including Grant, Lafayette, and Iowa counties in Wisconsin, Jo Daviess County in Illinois, and an irregular narrow belt of territory in Clayton and Dubuque counties paralleling the Mississippi River in Iowa. In this report a slightly smaller area is discussed, the region being limited on the east by the meridian of 90° west longitude. East of this meridian there are a few scattered prospects, hut comparatively little mining has been done in recent years in the area beyond the boundary indicated, so that it is sufficiently accurate for present purposes.