HYDEOLOGY. 109 



either the St. Peters or Potsdam sandstones can not be relied upon at 

 an elevation exceeding 15 feet above the lake surface, though Mr. 

 "Wild's well has demonstrated that it is possible at 50 feet. On the 

 other hand, however, the wells at Oshkosh show that the limit given 

 is the extreme one that is reasonably trustworthy. 



To the north of Lake Winnebago the limit in altitude descends at 

 about the same ratio as the general surface of the valley. It must 

 be remembered, however, that the St. Peters sandstone is not so relia- 

 ble in this region as farther south, where its thickness is more uni- 

 form. The Potsdam sandstone should, however, present reasonable 

 probabilities for the region along the Bay, at elevations not exceeding 

 25 or 30 feet above its surface, with slight chances for greater alti- 

 tudes. 



The third district lies in the valley of Rock river. An elevation 

 of 250 feet must be taken as the upper limit of favorable chances. 

 That a flow at this altitude is attainable is shown by the wells at 

 Watertown, Palmyra and Janesville. The St. Peters sandstone is 

 available for only a portion of the area that falls below that altitude, 

 since in some parts of it, this formation is deeply eroded by the 

 streams, and its fountain-forming possibilities destroyed. Success in 

 these portions will be chiefly dependent on the Potsdam sandstone. 



The list of elevations and the maps will be found indispensable to 

 an intelligent calculation of probabilities in this region, and something 

 more than wonted caution may here be recommended, because of the 

 nature of the formations, their nearness to the central anticlinal axis 

 of the state, and the presence of deep ancient river gorges now filled 

 and concealed by drift. 



As the majority of the deep seated wells of eastern Wisconsin de- 

 rive their flow from the St. Peters sandstone, it is important to know 

 at what elevation the upper face of that formation outcrops. The fol- 

 lowing list will supply the requisite data: 



ELEVATIONS OF THE JUNCTION OF THE ST. PETERS SANDSTONE AND TRENTON 



LIMESTONE. 



Rock County. 



Avon Feet. 



Sec. 5, N. E. qr., - - 272 



9, - - - 250 

 Beloit 



Sec. 3, S. W. qr., - 229 



3, S. W. qr.ofS. W. qr., 196 



10, N. E. qr., - - 180 



10, S. E. qr., - - 200 



Fulton 



Sec. 10, S. W. qr., - - 219 



Newville bridge, Eock river, - 208 



Rock County (con.) 



Magnolia Feet- 



Sec. 6, S. W qr., - 309 



7, S. E. qr., - - 433 



28, S. W. qr., - - 339 



R. E. cut, 330 

 Porter 



Sec. 9, N. W. qr., - 250 

 Eock 



Sec. 32, 189 



Alton, - - - - 208 



