670 GEOLOGY AND TOPOGRAPHY OF THE LEAD REGION. 



as are formed in river valleys by changes of level, have anywhere 

 been observed. This is most readily seen in those districts where it 

 becomes the surface rock over any extended portion of country. 



About the head waters of Grant river, in the towns of Fennimore, 

 Lancaster and Mount Hope, the country is an undulating prairie, 

 where the hills are sandstone, capped with a little Buff limestone, the 

 greater part of that formation having been denuded. Here the St. 

 Peters can be seen, its upper beds jutting out in low ledges, which 

 may be traced by the eye continuously for long distances, about the 



heads and sides of the small valleys. 



Q Such exposures are very fre- 



quent in Green county, where, 

 addition to the continuous 

 exposures, small hills are fre- 

 quently seen, with flat tops, 

 which have been denuded near- 

 ly down to the St. Peters. The 

 accompanying sketch represents 



SKETCH or A HILL IN THE TOWN OF MT. PLEASANT. a Section 01 SUCI1 an exposure, 

 1. Soil and clay. 2. Buff limestone. 3. St. Peters and is taken f rom a tract of 



eandstone - country in the town of Mt. 



Pleasant, in Green county, lying about the little Sugar river. The 

 characteristics are the cliff exposure at A, the steep slope of the 

 hill from A to B, and the table land of Buff limestone covered with 

 soil at C. 



The varying hardness of the upper bed of the St. Peters, some 

 portions, especially the white, being quite soft and friable, and 

 others nearly as hard as quartzite, due, perhaps, to its greater or less 

 impregnation with iron, appears to have caused an unequal resistance 

 to disintegration, which has resulted in the formation of Knobs, 

 as they are called. They are isolated pillars of sandstone, which shoot 

 up in picturesque castellated forms, frequently exposing the entire 

 thickness of the formation, and forming very conspicuous objects in 

 the landscape. They are chiefly found north of the dividing ridge, 

 about the tributaries of the Wisconsin. The following are the most 

 remarkable instances: 



(1) The Knobs, situated at the K W. cor. of Sec. 21, T. 7, R. 4 

 E. They are two conical hills of sandstone, forming the termination 

 of a ridge extending out from the west. They exhibit the full thick- 

 ness of the formation, which is here about 100 feet. 



(2) Castle Rock, situated in the southwest corner of the town of 

 Blue River. There are here two very high and precipitous hills of 



