GEOLOGICAL PAPERS 93 



(i) 200 feet of Pottsville. 



(2) 220 feet of Niagara. 



(3) 178 feet of Maquoketa. 



(4) 350 feet of Galena-Trenton limestone. 



Well Xo. 31. Peru Beer Co., about one-quarter mile west of 

 Xo. 30. shows : 



(1) 55-60 feet of Pottsville. 



(2) 400 feet of limestone and dolomite, the upper part is calcareous 



and possibh- Devonian. 



(3) 180 feet of Maquoketa shale. 



C4) 170 feet of Galena-Trenton limestone. 



Well Xo. 15, St. Bede College, one and one-half miles west of 

 Xo. 31: 



(i) 50 feet of Pottsville. 



(2) 450 feet of dolomite, the upper part of which is possibly Devonian. 



(3) 250 feet of Maquoketa shale. 



(4) 308 feet of Galena-Trenton. 



(5) 130 feet of St. Peters. 



At Spring ^*alley, well Xo. 14, water is obtained at a depth 

 corresponding to that of the Galena-Trenton limestone, well 

 Xo. 13. 



Artesian well X'o. 2 of Mineral Point Zinc Co., at DePue, 

 examined by Dr. J. A. Udden, and reported in correspondence 

 to the Director of the State Geological Survey : 



(i) Pottsville, 10-20 feet. 



(2) Dolomites, 231 ft., white and cream colored. Dolomite different 



from usual Xiagaran. Xo strong evidence to show that it is 

 Devonian, hence placed in the Niagaran. 

 Dolomitic limestone, white and straw colored, 243 feet. 



(3) Maquoketa shale, 170 feet. 



(4) Galena-Trenton, 258 feet. 



On the chart showing several of the logs just described a num- 

 ber of interesting details are brought out. The most significant 

 of these is the excessive and local thickness of the Pottsville sedi- 

 ments as shown in logs X'os. 16 and 2/. The condition as shown 

 by these records indicate that in Pottsville times there existed a 

 deep depression probably lying parallel to the axis of the La 

 Salle anticline, extending up from the south, but not present to 

 the west, as is shown by the thinning out of the formation in 

 that direction. The second noteworthy feature is the thinning of 

 the X'iagara limestone where the Pottsville is thickest. This 

 seems to indicate that the depression or basin in which the Potts- 

 ville sediments were deposited was not due to down faulting or 

 folding, but to extensive erosion in the X^iagara and Devonian 

 limestone. In pre-Pottsville times there apparently existed in the 



