HYDROLOGY. 159 



The Lake Winnebago System. All the drift wells of Oshkosh, Fond 

 du Lac, Taycheedah, Calumet, and their vicinity, may be considered as 

 constituting one group, owing their origin to the basin-shaped de- 

 pression occupied by the lake, the superficial layer of which is imper- 

 vious and prevents the w r ater from escaping into the lake until pierced. 



The wells at Green Bay and other points in the valley of the lower 

 Fox river derive their flow from, at, or near the surface of the rock, 

 and may be classed with the above system. 



The Poygan Lake System. The numerous wells in Rushford, 

 Aurora, Poysippi and vicinity, are located in part in the valley of the 

 Fox river, but they all belong to a common depression filled by a con- 

 tinuous lacustrine clay deposit, and are essentially alike in nature and 

 origin. They all belong to the drift, and owe their existence to the 

 alternate porous and impervious character of the red clay and associ- 

 ated beach deposits. The surface of the area is level and considerably 

 below that of the surrounding country. The flow is obtained at vari- 

 ous depths, but not without some degree of uniformity, giving rise to 

 the popular terms " forty foot vein " and " eighty foot vein." The 

 wells rarely exceed 100 feet in depth. 



The material penetrated is usually red clay, with occasional seams 

 of sand and gravel, the whole attaining a thickness of from 80 to 100 

 feet. There seems good reason for considering the " forty foot vein " 

 as being derived from the beach deposit between the upper and lower 

 red clays hereafter to be described, and the " eighty foot vein " as 

 corresponding to the beach formation between the lower red clay and 

 the blue bowlder clay. These beach deposits are preeminently porous 

 and water-bearing elsewhere in the state, and from the nature of the 

 led clay it would be difficult to account for two veins so persistent as 

 these seem to be, on any other supposition. These wells frequently 

 interfere with those near them so that it is necessary to adjust the 

 penstocks to the same level. This shows that they are derived from 

 a common stratum, and lends support to the view given above. The 

 flow is usually brisk and abundant, and in some cases is very copious. 

 The water is mostly excellent and generally rather soft. Occasionally 

 it is impregnated with iron and sulphur. 



The source of the flow of these wells is quite obvious. The clay 

 strata terminate on the margin of the basin adjacent to and in asso- 

 ciation with sandy drift hills of highly absorbent character. Around 

 the rim of the basin thus constituted the water finds access to the 

 porous layers and through them supplies the fountains. The num- 

 ber of these wells is large and constantly increasing, as the clay may be 

 bored with the greatest facility and at trifling cost. 



