222 Cincinnati Society of Natural History. 
S. 35° E. to S$. 81° W. In Columbia county, from W. to $8. 85° W., 
and 8. 47° W. In Sauk county, from S. 50° W. to S. 85° W.; and in 
Green Lake, 8S. 68° W. 
In southwestern Wisconsin, there is a driftless region of more than 
12,000 square miles, or about one-fourth the entire area of the State. 
Drift strize and drift materials are absolutely wanting. The topogra- 
phy of the country shows that it was never invaded by the drift. 
Except in the level country of Adams, Juneau, and eastern Jackson 
counties, it is everywhere a region of narrow, ramifying valleys, and 
narrow, steep-sided, dividing ridges, whose directions are toward every 
point of the cémpass, and whose perfectly coinciding horizontal strata 
prove conclusively their subeerial erosion. The ravines are all in direct 
‘proportion to the relative sizes of the streams in them, 
The altitude of the country seems to have performed no part in the 
causes which kept the drift from this extensive tract of country, for 
north of the head of sugar river, the limit crosses high ground, and the 
altitudes east of the limit are as great as those to the west; Sauk 
prairie is crossed on a level. Where the quartzite range north of Sauk 
prairie is crossed by the limit, it is higher (850 feet above Lake Michi- 
gan), than any part of the driftless area, except the Blue Mounds, 
whilst east a few miles, drift is found at 900 feet in altitude. From 
the limit near the east line of Adams county, the country, for 40 miles — 
to the west, is from 100 to 200 feet lower. From the northwest part of — 
Adams county, to the Wisconsin river, the limit is in a level country ; 
whilst from the Wisconsin westward the country north of it is every- 
where much higher than that to the south, the rise northward continu- 
ing to within 30 miles of Lake Superior. It thus appears that the 
driftless area is in a large part lower than the surrounding drift- 
covered country. Moreover, there is a scantiness of the drift from 29 
to 75 miles north of the driftless area. 
Roland D. Irving* said, the lacustrine clays extend inland from 
Lakes Michigan and Superior for many miles, and reach elevations of 
several hundred feet above the lakes. They are stratified beds of loose 
material, chiefly marly clays, with more or less sand, some gravel, and — 
a few bowlders. They were deposited, evidently, when the lakes were 
greatly expanded beyond their present limits. In the Central Wiscon- 
sin district, the lacustrine clays have only a small development, most 
of the district being either too high to have been reached by the lake 
depositions, or else lying behind the dividing ridges. The eastern 
* Geo. of Wisconsin, vol. ii. 
