4:50 GEOLOGY OF CENTRAL WISCONSIN. 



once prairie have been invaded by a timber growth, which has come 

 in since the settlement of the country, having been in former times 

 checked by the annual prairie fire's. Very large areas in Adams 

 county, for instance, which are now covered with a thick growth of 

 small oaks, are said to have been open prairies at the time of the first 

 settlements. The prairie areas are by no means always flat; indeed, 

 the flat prairies are the exception, and have chiefly been noticed along 

 the bottom land of the Wisconsin river. The ordinary prairie, how- 

 ever, as in northern Dane and eastern Columbia county, is very roll- 

 ing, commonly showing abrupt changes of level, even up to fifty or 

 a hundred feet. These changes in level are, in places, due to heaped 

 up drift, but more commonly to unequal denudation of the rocky 

 strata. In many cases, as, for instance, in the town of West Point, 

 Columbia county, the prairie area includes both lowland and bold 

 outlying bluffs, as much as two hundred or even three hundred feet 

 in height. The Central Wisconsin prairies are, with one notable ex- 

 ception, of small size, occupying at most not more than two or three 

 sections. The exception is the limestone prairie belt which occupies 

 large portions of the towns of Springfield, Westport, Dane, Vienna, 

 Windsor and Bristol, in northern Dane county; and of West Point, 

 Lodi, Arlington, Leeds, Hampden and Lowville, in Columbia county. 

 The same belt, though somevvhat broken in the towns of Otsego and 

 Courtland, continues to the northeast and passes into Green Lake 

 county. This large prairie area is for the most part on high land, 

 occupying the summit of the watershed between the Wisconsin and 

 Rock rivers. It is nearly always underlaid by the Lower Magnesian 

 limestone, whose irregular upper surface contributes much to the 

 rolling character of the prairie. 



The marshes are widely scattered, occurring over both the Archsean 

 and Silurian areas, though more numerously in the former. As a 

 general rule they are small, but in some cases are of very considerable 

 size, as, for instance, those extending along Duck creek and the up- 

 per Fox river east of Portage, which are many miles in length, and the 

 great marsh south of Plover, in Portage county, which covers the 

 greater part of four townships. Many of these marshes, as, for in- 

 stance, the Plover marsh just alluded to, are underlaid by a valuable 

 quality of peat. 



With regard to timber, it may be said that all of the counties of 

 Dane, Columbia, Sauk (except on the quartzite bluffs), Juneau, 

 Adams, Marquette and Waushara (except on the east), are covered 

 by a prevailing growth of small oaks; whilst Marathon, Portage, 

 eastern Waushara, most of Wood, Clark, and much of Jackson, are 



