2 INTRODUCTION. 



The State of Wisconsin lies between the parallels of 42° 30' and 47° north 

 latitude, and between 87° and 93° of longitude west from Greenwich; or it extends 

 from the State of Illinois on the south to Lake Superior on the north, and from 

 Lake Michigan on the east to the Mississippi and St. Croix rivers on the west. 

 Its area is about 55,000 square miles. About three-fifths of the State lie in the 

 basin of the Mississippi ; and the remainder is drained by the streams tributary to 

 the waters of the Great Lakes — Superior and Michigan. The former portion is 

 naturally divided into five great valleys, occupied by as many principal streams — 

 the St. Croix, Chippewa, Black, Wisconsin, and Kock rivers. The latter may be 

 divided into three parts — that drained directly into Lake Michigan, the basin of 

 Green Bay and its tributaries, and that which is drained into Lake Superior. 



These several hydrographical basins indicate also the general topography of the 

 State. The dividing grounds between the basins attain usually but a slight eleva- 

 tion above the surrounding country; so that it frequently happens that a lake or 

 marsh is drained in two opposite directions, and the water sent towards the ocean 

 at widely different points. These water-sheds, or " divides," as they are called, 

 attain their greatest elevation about the sources of the Montreal Kiver; where 

 there is found a continuation into Wisconsin of the Porcupine Mountains of the 

 Lake Superior Mining District. At one point near this place, the ridge is about 

 ],150 feet above Lake Michigan;-^ while at the western boundary of the State it is 

 diminished to about 500 feet. The region around the source of the Wisconsin 

 Kiver is a grand summit, from which the rivers flow in every direction like the radii 

 of a circle. They run into the Mississippi Kiver, Lake Superior, and Green Bay. 



The surface of Wisconsin may be characterized as nearly level, or gently 

 rolling, except along the banks of the Mississippi, and the lower portions of 

 some of its principal tributaries, where it is more broken, and where steep rocky 

 cliffs and precipitous hills abound. There are also prominent peaks in this region, 

 which tower above the general surface, so as to form conspicuous objects in the 

 landscape; of these the Blue Mounds are the most elevated, being 1,224 feet above 

 Lake Michigan. 



There is a ridge of broken land running from near the peninsula between Lake 

 Michigan and Green Bay, in a southwesterly direction, through the western parts 

 of Manitowoc, Sheboygan, Washington, and Waukesha counties, and thence into 

 Walworth and Rock counties. It is from three to five hundred feet in height, 

 with an occasional peak of even eight hundred feet above Lake Michigan, and 

 consists of irregular elevations and depressions throughout its whole course. At 

 places the depressions are more regular, and from their round form are called "pot- 

 ash kettles." They are doubtless owing to the decay and gradual washing away 

 of the soft and easily decomposed limestone by which the ridge is probably under- 

 laid. 



Another prominent feature in the topography of Eastern Wisconsin, is the cliff 

 or escarpment of limestone resembling the " mountain ridge" of Western New 



U. S. Geological Reports. 



