THE THURM AN -WILSON FAULT 



38s 



the genera] dip of the strata in that quarter of the state. North 

 of the fault the upthrow side has been removed by erosion till 

 no esacrpment has been left, while on the downthrow side the lesser 

 amount of erosion has left strata far to the east, with offset of 

 thirty-five and a half miles. North of the fault plane the strata 

 beneath Lewis, Cass County, are seventy feet thinner than recorded 

 in the log of the deep well at Clarinda, Iowa; and south of the fault 



Fig. I 



plane they diminish in thickness 235 feet further within a distance 

 of 41 miles from Briscoe, Adams County, to the ''Backbone" west 

 of Winterset, in Madison County. The most marked thinning is im- 

 mediately beneath the Oread limestone, where in Missouri Hinds and 

 Greene report a faunal break.^ This is to be noted in contrasting 

 a section northeast-southwest north of the fault plane with a par- 

 allel section south of the fault plane. The section from Reno to 

 Briscoe across the fault plane connects these two sections (Fig. 2). 



' Hinds and Greene, "Stratigraphy of the Pennsylvanian Series," Missouri Bureau 

 of Geology and Mines, XIII (2d series, 1915), 155. 



