m^ 



Artesian Well Boring in Southeastern Minnesota — Hall. 135 



Brownsville well and by several Iowa wells which have penetrated 

 what I presume is the same sandrock.* 



The St. Croix series, as a whole, is of great extent and 

 thickness. In southeastern Minnesota it is found everywhere 

 that the overlying rocks occur, and whenever it has been pene- 

 trated, water has been found in it. It measures up to 478 feet in 

 thickness at East Minneapolis, and over 400 feet at Hastings. In 

 Wisconsin, according to Professor Irving, the rocks which in 

 Minnesota are included in the St. Croix, reach a thickness of 700 

 feetf and are chiefly sandstones. Large quantities of water are 

 obtained in the city of Madison by boring into these sandstones. 



14. The Potsdam Sa:n^dsto]S"e. — Beneath these three 

 formations which constitute the Saint Croix series, sandstones 

 still continue. They possess a red color, and vary considerably 

 in texture; some of them are coarse enough for conglomerates, and 

 others are fine like shales. This series is waterbearing like those 

 above it; indeed it could not well be otherwise. These rocks are 

 conformable with those above them so far as our investigations 

 enaole us to determine. 



Mr. Upham regards this series as the westward extension of 

 what is called in New York the Potsdam formation, and he would 

 give it the same name in this state which it has carried in New 

 York and along the south shore of Lake Superior for so many 

 years. It "constitutes a floor upon which the lowest member of 

 the Saint Croix was laid in nearly uniform thickness" throughout 

 southeastern Minnesota and over a large extent of Wisconsin and 

 Iowa and other western states. 



The thickness of the Potsdam is difficult to niake out. At 

 East Minneapolis it must be at least 1,050 feet. At Mankato the 

 borings from 915 feet to the bottom, 2,204 feet, disclose these red 

 sandstones and shales, a thickness of 1,289 feet, and the underly- 

 ing rocks were not reached. But to the southeast the sandstones 



*T take the following notes from Upham: 



It is 550 feet to the granite at La Crosse, Wis. 

 u u 750 u u « u u Lansing, la. 

 ""1,475 " " " " " Mason City, la. 

 There is here no flow, but water in abundance comes within 28 feet of 

 the surface. It is 1,250 feet to the granite at Decorah, la. No flow of water, 

 but it comes within 20 feet of the surface. At Calmar, 10 miles from 

 Decorah, and 300 feet higher, boring ceased at 1,223 feet in sandrock. An 

 inexhaustible supply of water, not, however, rising to the surface. 



fGeology of Wisconsin, Vol. ii,p. 534. 



