656 GEOLOGY AND TOPOGRAPHY OF THE LEAD REGION. 



and Cincinnati groups; except in such localities as were protected bv 

 a superior hardness of some part of the formation, as in the case of 

 the Blue Mounds. 



The result of the denudation has been to divide the country into 

 two parts, each differing widely from the other in its topographical 

 features. The streams flowing southward from the watershed have 

 eroded the country into gently undulating slopes. This is probably 

 due to the direction of the streams conforming in a measure to the 

 dip of the strata. Abrupt cliffs and steep ravines are the exception, 

 and not the rule, never being found in the immediate neighborhood 

 of the watershed, but rather confined to the small lateral branches. 

 On the other hand, to the north of the watershed, the panorama of 

 bluffs and precipitous ravines is almost mountainous in its aspect. 

 In fact, nothing can be more striking than the contrast which pre- 

 sents itself, from certain points on the divide, in looking from north 

 to south. In nearly all of the ravines leading northward, the fall of 

 the first quarter of a mile is not less than one hundred feet; and, in 

 general, it is true of the streams flowing northward, that three- 

 quarters of the fall takes place in the first quarter of the distance 

 from their sources to their mouth. 



It seems not improbable that these sudden declivities are due to the 

 streams flowing over the edges of the strata, rather than lengthwise 

 along their dip. Again, the streams flowing to the southward become 

 comparatively sluggish in their course, as soon as they cease to be 

 brooks. They have usually a soft muddy bottom, while those tributary 

 to the Wisconsin are clear and rapid streams, flowing over a sandy 

 or gravelly bottom, their valleys being narrow and their sides very 

 steep. 



The streams tributary to the Platte, Grant and Pecatonica rivers do 

 not exhibit any marked characteristics on one side that are not shared 

 equally by the other. It may be remarked, however, that the short 

 streams, which flow into the Mississippi river, present much the same 

 topographical characteristics as are seen in the southern tributaries 

 of the Wisconsin, narrow and deep ravines and valleys, being ap- 

 parently the rule in the western part of Grant county. 



The Platte river is frequently found inclosed by hills which are 

 gently sloping on one side, and quite precipitous on the other. This 

 is especially noticeable near its mouth. The river in such cases seems 

 to have encroached on one side of the valley for a long period of 

 time, producing a cliff exposure of Lower Magnesian near the river, 

 and a steep bank of St. Peters, capped with a more retreating slope of 

 the Trenton, as shown in the following section. [See Fig. 1.] 



