TOPOGRAPHY. 103 



little doubt that the stream would follow its course along the strike of 

 the formations, at least as far as the moraine in Wai worth county. 

 Beyond that point the drift is so deep as to preclude any knowledge 

 of the configuration of the rock surface. 



It is interestino- to notice that this river, which has been following 



O * O 



the trend of a soft, easily eroded formation the Cincinnati shale 

 from which it is now forced by drift, passes across the Galena and 

 Trenton limestones and makes its bed in the next lower soft forma- 

 tion, the friable St. Peters sandstone, which it follows, until it leaves 

 the state. 



Considering the Rock river valley as an extension of that of Green 

 Bay, the two forming one great excavated trough, the elevations it 

 attains become matters of much geological and commercial import- 

 ance. At the north, it finds in Green Bay the level of Lake Michi- 

 gan and, as has been previously remarked, rises somewhat rapidly 

 about 1TO feet to Lake Winnebago. Throughout the length of that 

 lake, a distance of thirty miles, it is essentially level. From its 

 southern extremity, the valley again rises about 140 feet to the wat- 

 ershed, making its greatest elevation a little over 300 feet. 1 The 

 former Lake Horicon was 285 feet above Lake Michigan. From this 

 point a gentle declivity brings the valley down to 150 feet, at Beloit, 

 on the state line. It continues its moderate descent till it joins the 

 Mississippi, where it is about 50 feet below Lake Michigan. This 

 Illinois extension of the valley differs, however, somewhat widely iii 

 geological and topographical features from the portion in Wisconsin. 



The commercial importance of the foregoing facts is very consid- 

 erable as now realized, but is far greater in its future possibilities. 

 It furnishes important facilities for both land and water communica- 

 tion. The sagacious proprietors of the Chicago & Northwestern 

 Railway early perceived this and located nearly 200 miles of their 

 road in this valley, thus securing an easy grade along a line of im- 

 portant towns, supported by an exceedingly rich agricultural region, 

 and possessing some of the finest water powers of the interior. 



Water communication is utilized to some extent, but the great pos- 

 sibilities in this direction lie yet undeveloped. In the year 1866, a 

 survey of this valley from Fond du Lac to the Mississippi was au- 

 thorized by the general government and executed by Col. James Wor- 

 rall, under the direction of Gen. J. EL Wilson, having for its object 

 the determination of the practicability of establishing a capacious 



1 All elevations in this report, unless otherwise designated, signify altitude above Lake 

 Michigan, which, awaiting more accurate measurements, is considered 578 feet above 

 the ocean. 



