SOME PARTLY DISSECTED PLAINS IN JO DAVIESS 
COUNTY, ILEENOTS: 
ARTHUR C. TROWBRIDGE 
State University of Iowa 
Jo Daviess County is the northwesternmost county in Illinois 
and adjoins northeastern Iowa and southwestern Wisconsin. The 
county is partly covered by the Galena and Elizabeth topographic 
sheets of the United States Geological Survey. The topography 
of this county occupying the southern part of the driftless area has 
remained unaltered by the ice invasion and is still exposed for 
physiographic study. The writer, in company with E. W. Shaw 
and B. H. Schockel, spent a large part of the field season of 1910 
in Jo Daviess County in co-operative work between the United 
States Geological Survey and the Illinois Geological Survey, and the 
following paper is one result of that work. 
Rock formations appearing at the surface in the district are of 
Ordovician and Silurian age, and are classified as follows: 
Name of Formation Kind of Rock Thickness 
INAS ALAR. ites cued laches Ot soils © Dolomite 140 feet 
Mia MOK EEA tert can aoa cles os dere. ts Shale 108-209 feet 
(GAS, ene ee ne Dolomite 246 feet 
lattevilles amie sce 8. aude ee ae ses Limestone 50 feet 
All of these formations occur at the surface over wide areas, with 
the exception of the Platteville, which is found only in the valley 
of Galena River in the northern part of the district. The strata 
have a general dip to the southwest of about 17 feet to the mile, 
and on this monoclinal structure are a series of slight, hardly 
noticeable anticlines and synclines. 
The most conspicuous topographic feature in the county, 
aside from the bluffs of the Mississippi Valley, is a more or less 
* Published by permission of the Director of the Illinois Geological Survey. 
731 
