150 GEOLOGT OF EASTERN WISCONSIN. 



depth. It will promote clearness of understanding to call to mind the 

 requisite conditions which will be found more amply stated in Yol. I. 

 They are as follows: There should be an impervious stratum to pre- 

 vent the escape of the water below; a previous water-bearing stratum 

 upon this to furnish the flow of water; a second impervious layer 

 upon this to prevent the escape of the water above, it being under 

 pressure from the fountain head. These must dip, and there must be 

 no adequate outlet for the water at a lower level than the well. There 

 must also be a sufficient collecting area or reservoir in connection 

 with the porous stratum and it must have sufficient elevation to act 

 as a fountain head. As these wells depend for their essential con- 

 ditions upon the character of the strata, it will be necessary to antici- 

 pate some things subsequently given in connection with the formations 

 involved. To these, the reader, who desires a more perfect under- 

 standing than can be obtained from the necessarily brief sketches 

 that follow, is referred. It would doubtless best subserve the interest 

 and convenience of the general reader, to classify the numerous wells 

 according to the formation from which they derive their flow, and to 

 treat them as thus grouped. Were this method pursued, the classes 

 would be six in number, as follows: 



1. Those that derive their flow entirely from the drift, clay layers 

 forming the upper and lower confining strata and sand or gravel the 

 the water-bearing seam. The last is usually a beach deposit and at 

 least one of the others a lacustrine clay. This group includes the 

 fountains of Taycheedah, Calumet, Poysippi, Rushford, Auroraville, 



Whitewater, Byron, and a part of those of Fond du Lac, Oakfield, 

 and Oshkosh, with some in the vicinity of Lake Michigan. 



2. Those that derive their flow from the junction of the drift 

 with the indurated rocks below. In these the drift clays resting on 

 the rock constitute the upper confining stratum and the subjacent for- 

 mations, the lower, while a layer of sand or gravel or the open nature 

 of the rock surface affords passage for the water. This class includes 

 most of the fountains at Fond du Lac, Oshkosh, Oakfield, and Green 

 Bay. 



j. Those that originate in the Niagara limestone. This body of 

 limestone furnishes in itself, locally, the necessary pervious and iia- 

 pervious strata. The Manitowoc wells belong here. 



^. Those that arise from the Galena and Trenton limestones. 

 These formations, like the Niagara, aided by the overlying drift, pre- 

 sent all the needed conditions. There are embraced here, most of the 

 Watertown fountains and a portion of those at Oshkosh and Fond 

 du Lac. 



