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 Walworth county. 

 Beyond that point the drift is so deep as to preclude any knowledo-e 

 of the configuration of the rock surface. 



It is interesting to notice that this river, which has been foUowiu':'- 

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

 from which it is now forced by drift, j^asses across the Galena and 

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

 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 170 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.^ 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 difi'ers, however, somewhat widely in 

 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 & ]N"orthwestern 

 Eailway 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. H. Wilson, having for its object 

 the determination of the practicability of establishing a capacious 



' AU elevations in this report, unless otherwise designated, signify altitude above Lake 

 Midiigan, which, awaiting more accurate measurements, is considered 678 feet above 

 tiie ocean. 



