Artesian Well Boring in Southeastern Minnesota — Hall. 131 



sand or gravel over an area sufficiently large to catch and carry 

 a supply of v^rater. 



2. The Cretaceous. — Cretaceous rocks are found in a few 

 places in this state. They are sandstones, shales, clays and car- 

 bonates. The extent of these rocks is not great, and mere isolated 

 areas have thus far been found. This formation is not distin- 

 guished as a water-bearing one for deep wells. 



3. The Devonian is equally insignificant from the standpoint 

 of the well- borer. It occurs only in the southern portion of the 

 state, so far as known. Its outcrops lie in Fillmore and Mower 

 counties, with possibly some beds to the east and west of this cen- 

 tral location. Doubtless the rocks of this formation are lime- 

 stones and dolomites. 



4. The Trenton. — The Lower Silurian represented by the 

 Trenton limestones and shales is the next in order of the Paleozoic 

 rocks. This is a bed of 30 feet in thickness, more or less, and it is 

 a persistent one. The upper part of it is very impure limestone, 

 containing some fossils* and lying nearly horizontal over a con- 

 siderable portion of southeastern Minnesota. Its extent is not so 

 great as that of the underlying Cambrian rocks, although it is 

 found in Hennepin, Ramsey and Washington counties and thence 

 southerly in Dakota, Goodhue, Rice, Steele, Dodge, Olmsted, 

 Winona, Fillmore and Houston counties, and very probably in 

 Wabasha and Mower. While this formation is quite impervious, 

 it is interrupted through the erosion of streams and thus does not 

 afford a satisfactory covering for the porous stratum beneath it. 



5. The St. Peter sandstone lies next beneath the Trenton 

 limestone. To the north this formation reaches beyond Minneapo- 

 lis on the Mississippi, but it is too high to be seen in the banks of 

 the St. Croix river. It is found in the central portions of Wash- 

 ington county, where it is protected from erosion by the overlying 

 Trenton limestone. For some miles southward from St. Paul it 

 has been eroded to a considerable extent, but still remains in a few 

 isolated knolls or buttes in Dakota county. It again comes In as a 

 quite persistent formation in eastern Rice, Goodhue, Steele, Dodge^ 

 Olmsted and Fillmore counties. It is more than likely that this 

 rock may underlie parts of the following counties in addition:; 

 Wasena, Winona, Houston, Mower and Freeborn. It certainly 

 occurs in the western part of Wino na ^nd Houston, and must run 



*This Bulletin page 115. 



