HYDROLOGY. 135 



example, that of the East Branch of the Rock river, which joins the 

 main stream in Horicon marsh. 



This river has its source in a broad, deep valley, extending from the 

 southeast to the northwest (about N. 30 W.) for a distance of up- 

 wards of 20 miles. In the towns of Wayne, Theresa, and Lomira, the 

 width is from one to two miles between the foot of the hills that rise 

 somewhat abruptly on either side. The valley is occupied very ex- 

 tensively by marsh. Branches from the north and south unite near 

 the center and form the main stream, which taking a direction nearly 

 at right angles, and pursuing a serpentine course among the parallel 

 north and south ridges of this region, finally discharges its waters 

 into Horicon Marsh, thus forming a rude italic T, the upper portion 

 being formed by the branches first mentioned. These branches are 

 not large, nor is the area drained by them considerable. The valley 

 which they occupy may be traced onward to a northward connection 

 with the valleys crossing the ledge in Byron. 



It is scarcely credible that this valley with all its peculiarities was 

 due to the unaided erosion of the streams occupying it. Though par- 

 tially filled with drift accumulations, it is really channeled from the 

 Niagara limestone, which distinguishes it from the class last under 

 consideration, where the essential condition was two formations of 

 different resisting power. In explaining its origin we must again 

 have recourse to glacial action. We find that the drift movement was 

 southward along the axis of Lake Winnebago, but on surmounting 

 the ledge on the east and south, it turned somewhat eastward and fol- 

 lowed down the slope of the surface and dip of the rocks, eroding fur- 

 rows that have a southeasterly trend. One of these is the valley in 

 question, which is doubtless more extensive and well defined than the 

 adjoining ones, because it lies south of Lake Winnebago, that is, more 

 nearly in the line of heavy glacial action. The angle in the ledge just 

 north of it doubtless contributed to the same result. 



Relationship of some of the streams on opposite sides of the 

 Kettle Range. One further feature relating to certain streams and 

 their attendant topography deserves notice. It consists of a certain 

 peculiar and definite correlation between the streams on the east and 

 west sides of the great dividing drift ridge. 



Where an extended ridge-like watershed exists, it is to be expected 

 that streams on the opposite sides will rise near each other and flow 

 in opposite directions, at right angles to the ridge, but in the present 

 instance they are arranged in pairs, and connected across the summit 

 by more or less well defined valleys, so that the relationship cannot 

 be looked upon as being merely fortuitous. 



