548 



F. T. THWAITES 



The thickness of the Trempealeau formation is at a minimum 

 of 35 feet in northeastern Wisconsin; in the southwestern district 

 it exceeds loo feet. The record shown in Table IV is typical of 

 northeastern Wisconsin. 



TABLE IV 



Partial Log of State Reformatory Well, Green Bay, Wisconsin 



MAZOMANIE FORMATION 



Distribution. — ^The Mazomanie sandstone is known from far 

 northeastern Wisconsin to near Spring Green, Wisconsin. It is 

 a rather firm rock and forms conspicuous crags among which may- 

 be mentioned . the Natural Bridge, west of Prairie du Sac. A line 

 drawn from Spring Green east of north through central Adams 

 County separates the Mazomanie from the Franconia. The 

 Mazomanie thins out to the west and overlaps the older Franconia 

 for distances of 10 to 20 miles. Good examples of Mazomanie 

 overlying Franconia can be found near Reedsburg and Friendship. 



Character, — The Mazomanie consists of fine to medium grained 

 gray to dark red sandstone, irregularly cemented by dolomite; 

 locally there are beds of red, green, and gray calcareous shale. 

 At depth some layers are so well cemented that they break into 

 chips under the drill and are hence reported as Umestone in drillers^ 

 logs, or described as sandy dolomite by some geologists who have 

 examined samples. At Markesan and Green Lake, Wisconsin, the 

 base of the Mazomanie consists of gray dolomite with purple spots, 

 very similar to the St. Lawrence member of the Trempealeau. 

 The red colors are of local distribution; they are mainly found in 

 northeastern Illinois. The entire formation contains more or less 

 glauconite and that mineral is most abundant near the top. This 

 fact makes the Mazomanie a valuable marker in the geological 

 column. The record is typical of the Mazomanie of eastern 



