o26 Tertiary. 



S. 35° E. to S. 81° W. In Columbia county, from W. to S. 85° W., 

 and S. 47° W. In Sauk county, from S. 50° W. to S. 85° W. ; and in 

 Green Lake, S. 68° W. 



In souttiwestern Wisconsin, there is a driftless region of more than 

 12,000 square miles, or about one-fourth the entire area of the State. 

 Drift striae and drift materials are absolutel}' wanting. The topogra- 

 ph}' of the countr^^ 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 ever^^ 

 point of the compass, and whose perfectly coinciding horizontal strata 

 prove conclusively- their subserial 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 b}' 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 lovver. From the northwest part of 

 Adams county, to the Wisconsin river, the limit is in a level countr^^ ; 

 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 thau the surrounding drift- 

 covered country. Moreover, there is a scantiness of the drift from 25 

 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 marl}^ clays, with more or less sand, some gravel, and 

 a few bowlders. They were deposited, evidentl}-, when the lakes were 

 greatly expanded beyond their present limits. In the Central Wiscon- 

 sin district, the lacustrine clays have onl}' a small development, most 

 of the district being either too high to have been i cached by the lake 

 depositions, or else lying behind the dividing ridges. The eastern 



* Geo. of Wisconsin, vol- ii. 



