PALEOZOIC ROCKS FOUND IN DEEP WELLS 



539 



Passing to the east, dolomite becomes more and more abundant 

 until near Beloit, Wisconsin, the entire group consists of buff and 

 blue dolomite; Sardeson proposed the name Beloit for the eastern 

 equivalent of the Decorah and Platteville formations. The 

 Galena formation is everywhere a dolomite; it is rather coarse 

 grained, gray at depth, and weathers to a yellow sandy consistency 

 near the surface. At its base in southwestern Wisconsin Ulrich 

 finds the Prosser formation of Minnesota. 



In northeastern Wisconsin less is known of either group. The 

 Galena is certainly present as a gray dolomite with some bluish 

 gray shaly partings. On lithologic grounds the entire thickness of 



TABLE I 



Partial Log of Waterworks Well, Cedarbtjrg, Wisconsin 



Dolomite, gray 



Dolomite, mixed gray and light blue 



Dolomite, gray 



Dolomite, mixed light blue and gray 



Dolomite, gray 



Dolomite, bluish gray and gray 



Dolomite, gray 



Dolomite, gray, sandy 



Total thickness 



Depth 

 (Feet) 



dolomites of that district can be divided into two divisions; of 

 these the upper is almost wholly gray and the lower is blue, mottled 

 blue and gray, and gray only in a few thin beds. Partings of blue 

 dolomitic shale are much more common throughout the lower 

 division. The well log shown in Table I is typical of this formation 

 in eastern Wisconsin. 



Too little is known of the outcrops in this region to warrant 

 the writer in attempting to correlate the succession found in wells 

 with the section to the southwest. Chert is conspicuous on all 

 weathered outcrops of both the Galena and Beloit formations but 

 is seldom met with in drill cuttings from eastern Wisconsin and 

 northeastern Illinois. The chert is gray or white at depth, although 

 weathered specimens assume a yellow color. In much of eastern 



