598 GEOLOGY OF CENTRAL WISCONSIN. 



depth which connects the ground about the west end of Lake Mendota with that 

 bordering the Wisconsin. The highest point of the valley is 85 feet above Lake Meii- 

 dota, and in it are streams running in either direction. Black Earth river the larger 

 of the two which runs westward to the Wisconsin, heads within three miles of Lake 

 Mendota, and at only 80 feet above its level. It has been suggested by Gen. G. K. 

 Warren in his report on the Fox and Wisconsin rivers, that this valley indicates a former 

 outlet, westward to the Wisconsin, of the Madison system of lakes. It is not impossible 

 that such an outlet may have existed, but there is nothing in the structure of the region 

 to show that we have here anything else than a case where two systems of erosion have 

 approached one another until the dividing ridge has been partially broken clown. South 

 of Black Earth river the high ground comes in again, and, taking a turn westward to 

 accord with the changed direction of the Wisconsin river, passes out of the district. 



To the north and west, in the towns of Dane, Roxbury and Berry, the dividing ridge 

 presents a very abrupt escarpment, which projects in long bold points into the valley of 

 the Wisconsin. Beyond the escarpment the low ground is occupied by numerous out- 

 lying patches of the high country of varying sizes, similar to those already described as 

 occurring in the adjoining towns of West Point, Lodi, etc., in Columbia county. 



Southward from the dividing ridge there is a general and much more gradual descent to 

 the south' and east, conforming with the descent in those directions of the underlying 

 strata. West of a line drawn centrally north and south through the county, the general 

 descent of both the country- surface and strata is southward only. East of such a line, 

 the line of greatest descent veers more and more to the eastward, until along the north- 

 ern part of the east line of the county, it is almost wholly in that direction. The drain- 

 age system corresponds with this general structure. In the northeast, in the towns of 

 York, Bristol, Sun Prairie and Medina, the drainage is eastward into Waterloo creek. 

 Farther south, in Cottage Grove, Deerfield and Christiana, the drainage is also eastward 

 towards Koskonong creek, which itself has a general southerly direction. In the central 

 part of the county the drainage along the Catfish valley is in a southeasterly direction, 

 whilst farther west, the Sugar river system runs almost exactly southward. In minor 

 detail, of course, the directions of the streams are due to other causes. 



The Catfish valley, with its chain of lakes, is the central topographical feature of the 

 county. The head- waters of the Catfish are a number of small streams which rise on 

 the south side of the divide in Springfield, Dane, Vienna and Windsor, and coine to- 

 gether in the southern part of the town of Westport. From here to the junction with 

 Rock river, the valley has a southeasterly course, a length of 27 miles, and a width from 

 high ground to high ground of from 4 to 9 miles. Its surface lies generally at from 250 

 to 300 feet above Lake Michigan, but is quite irregular, the irregularity being largely 

 due to considerable accumulations of drift, but also to the occurrence of small rock out- 

 liers, and to the projection into the valley on either side of low rock ridges. These have a 

 general northeast southwest trend, and tend to divide the valley into more or less sepa- 

 rate, parallel, cross-valleys, which are very marked, and are undoubtedly to be attrib- 

 uted to the movement over the country of glacier ice, to which cause also is to be assigned 

 the linear nature of the topography of all of the eastern part of the county. The several 

 lakes of the region about Madison are expansions of the Catfish into such cross-valleys, 

 the ridges between which here run entirely across the main valley, though not formed 

 throughout of rock material. Lake Mendota occupies two of the cross-valleys, partially 

 separated by the low ridge of Picnic point and McBride's point. Lake Monona lies m 

 one similar valley, which extends far to the southwestward, and holds also the smaller 

 sheet of water known as Dead Lake, or Lake Wingra. Further south, the glacial move- 

 ment had a more nearly southerly direction, and the directions of the cross- valleys cor- 

 respond. There is no prairie in the Catfish valley proper. Along the head streams in 

 Springfield, Westport and Burke, the marshes are of considerable extent. 



