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178 IOWA ACADEMY OF SCIENCE Vol. XXIV, 1917 
surface of the Prairie du Chien formation where cov- 
ered by the St. Peter has a relief of as much as two hundred 
feet. The roughness of this surface is illustrated south of 
Chien and St. Peter one and one-half miles south of Waukon Junction. 
Waukon Junction where it has a slope of eighty-four feet in 
fifty yards (figures 15 and 16), in the northwest corner of 
McGregor where its relief is one hundred nine feet in less than 
one-half mile, and at the Clayton sand pit, where it changes 
Fig. 16 — Diagrammatic sketch of the relations between the Prairie du 
Chien and St. Peter formations seven-eighths of a mile south of Waukon 
Junction. 
altitudes by an amount of fifty feet within the pit. The irreg- 
ularity of this surface is further illustrated by figures 17 and 
18, 
