\ 
PRAIRIE DU CHIEN-ST. PETER UNCONFORMITY IN IOWA 179 
(2) The thickness of each of the two formations varies 
greatly from point to point, but the sum of the thicknesses of 
the two at given places is practically constant and not far from 
300 feet. This is best shown at Pikes Peak and Pictured Rock. 
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1 >111 1 1 Pd j J l 1 I 
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Fig. 17— Diagram illustrating the conditions one and one-half, miles south 
of Church. 
The Prairie du Chien overlies the Jordan sandstone conformably 
along the Mississippi river at 632 feet above tide and on the 
slopes of Pikes Peak the St, Peter-Platteville contact is found. 
There are three trails leading from one of these contacts past 
the other, Three parties of students each making a traverse 
Fig. 18— Cross section of the' valley of Pictured Rock Creek. 
up one of these trails, with a handlevel, ascertained the thick- 
ness of the St. Peter and Prairie du Chien formations. All the 
time they were within shouting distance. The results are shown 
in the accompanying table. 
