LAND AND SEA OSCILLATIONS — ULRICH. 



335 



exposed in the bluffs east of Spring Green the Mazomanie sandstone, 

 as the new formation is called, is about 10 feet thick. Four miles 

 east of the town it has thickened to 80 feet, and at Fairy Bluff it 

 reaches 100 feet. Wherever it rises to considerable heights above the 

 valley bottoms in Dane, Sauk, and Columbia counties it forms cliffs, 

 which is not at all true of the typical Franconia. 



But, so far as positive evidence regarding the age relations of the 

 Franconia and the Mazomanie is concerned, these investigations of 

 the bluffs along the Wisconsin Kiver left the question as unsolved as 

 before. Nor did we come any nearer to its satisfactory solution in 

 the course of the following season's work when a series of sections 

 was made on the south side and around the eastern end of the 

 Baraboo Range. But just before the close of the field studies in 

 1918 some very promising but under the circumstances inconclusive 



IV£6T 



Mississippi Rjvo- 



C F BARAB OO 



Pilot Knob 



RANGE 



CNEOT.3 OCT. 



Fig. 4. — Section across central Wisconsin, showing greater eastward extent of the Fran- 

 conia in this part of the State and intercalation of the Mazomanie between the top of 

 the Franconia and the base of the St. Lawrence. 



observations were made in sectioning the outliers and bluffs which 

 dot the sandy plain of central Wisconsin. Namely, at one of these 

 bluffs I found a perfectly characteristic Mazomanie cliff and beneath 

 it a 2-foot exposure of reddish sandstone that seemed to me to be of 

 Franconia age. 



However, the evidence at this place was not satisfactory to Dr. 

 W. O. Hotchkiss, State Geologist, and Mr. F. Thwaites, who accom- 

 panied me on this as on most of the other trips through the State. 

 Their doubts arose mainly from the fact that my interpretation re- 

 quired the assumption of a fault hitherto unsuspected between this 

 bluff and Pilot Knob, which lies less than a mile to the northwest. 



And so it was left to the work of the past summer to clear away 

 all doubt, if possible. And it was cleared away. Other outliers in 

 this vicinity were visited until finally we found two that were capped 

 by Mazomanie and St. Lawrence and beneath the Mazomanie showed 



