THE THURMAN-WILSON FAULT THROUGH SOUTH- 

 WESTERN IOWA, AND ITS BEARINGS^ 



JOHN L. TILTON 



Simpson College, Indianola, Iowa 



WHY THE EXTENSION OF THE FAULT HAS BEEN OVERLOOKED 



It may seem remarkable that an important fault should extend 

 from near the southwest corner of Iowa to the central part of the 

 state, with indications that it may actually extend to the "Driftless 

 Area," and very little evidence of the presence of such a fracture 

 exist in the literature of the state.^ There are, however, reasons 

 for this lack of previous recognition. The strata of the Missouri 

 stage of the Pennsylvanian, in and beneath which nearly all of the 

 displacement in southwestern Iowa took place, is concealed over 



' Published with the approval of the director of the Iowa Geological Survey. 



2 The following important references may be noted: 



J. E. Todd, "On the Folding of the Carboniferous Strata in Southwestern Iowa," 

 Proceedings of the Iowa Academy of Science, I, Part I (1889), 61; "Some Varied Con- 

 clusions in Iowa Geology," ibid., XIII (1906), 184. 



G. L. Smith, "Carboniferous Section of Southwestern Iowa," Iowa Geol. Surv., 

 XIX (1909), 612. 



C. R. Keyes, "Controlling Fault Systems of Iowa," Proc. of the Iowa Acad, of 

 Sci., XXIII (1916), 103; "Extent and Age of the Cap-au-Gres Fault," ibid., XXIV 

 (1917), 61. 



Keyes's 1916 article was published during the summer, a year later than the field 

 work by which the present writer discovered that near Stennett the Thurman-Wilson 

 fault of Todd and Smith did not become an anticline but continued as a fault. In 

 Keyes's two papers he is chiefly concerned with the Fort Dodge and the Cap-au-Gres 

 faults, but in spacing the faults in his first paper he represents the "Red Oak fault" 

 (the term he uses for Todd and Smith's fault between Thurman and Wilson quarries) 

 as extending far to the northeast without giving any reason for opposing Smith's view 

 that the fault became an anticline near Stennett, and calls the throw four hundred 

 feet instead of three hundred feet, as reported by Smith. He also continues this fault 

 line west to Hebron, Nebraska, without stating his reason for disagreeing with the 

 geologists of Nebraska. However, it should be noted that near Bloomington in 

 Franklin County, about seventy-three miles west of Hebron, Professor Erwin H. 

 Barbour mentions and illustrates "one major and several minor faults of one to four 

 feet displacement" {Nebraska Geol. Surv., IV, Part VII, PI. 12). 



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