CENTRAL STABLE REGION OF THE UNITED STATES 



51 



A sag between Peru and Logansport across the arch is called the 

 Logansport sag, and many other minor irregularities make up the oil field 

 structures in the area. 



Findlay Arch 



The Findlay arch is the right arm of the Cincinnati dome, and extends 

 north-northeastward into the peninsular area of Ontario and thence to 

 the Canadian Shield (Plate 5). It is similar in size and relief to the 

 Kankakee arch and, since the early Ordovician uplift, it has had a similar 

 history (Cohee, personal communication). It was not an area where 

 thick pre-St. Peter sediments accumulated, and may actually have been 

 a low ridge of Precambrian rock at the beginning of Cambrian deposition 

 (Cohee, personal communication). 



The uplift along the Findlay arch was localized and of somewhat 

 greater magnitude than along the Kankakee arch (Cohee, personal com- 

 munication ) . The cross section, Fig. 5.4, shows the base of the Black River 

 and the progressive overlap northward to the Precambrian crystallines 

 of southeastern Ontario. 



The names Lima axis and Sandusky arch (Phinney, 1891), Algonquin 

 axis (Kay, 1942), and Cataract axis have been used for all or part of the 

 arch, but Findlay arch is preferred by Ekblaw ( 1938 ) and others. A sag 



in the axis near Chatham, as contoured by Cohee (personal communica- 

 tion ), reflects movements at the same time approximately as those in the 

 arch. The cross structure is called the Chatham sag. 



Arches of Central Kansas 



The geologic map of mid-Pennsylvanian time (Plate 7) shows the 

 superposition of one arch over another in central Kansas, with axes trend- 

 ing in slightly different directions. At the close of the Devonian, a broad 

 arch, for which the name Ellis is reserved (Moore and Jewett, 1942), 

 rose (Plate 5) and was eroded so that the Lower Ordovician Arbuckle 

 limestone was exposed in the core. The Mississippian seas then lapped 

 onto the Ellis arch and perhaps covered it. Post-Mississippian arching 

 in a somewhat more northerly direction and in a narrower zone resulted in 

 the erosion of the Mississippian strata and the exposing of the strata in 

 the Ellis arch again. This new uplift is called the central Kansas arch. 

 However, the local folds that developed parallel with the major axis of 

 the Ellis arch trend obliquely across the core of the central Kansas arch. 

 Examine the cross section of Fig. 5.13 and the map of Fig. 14.1. 



The Ellis arch continued eastward as the Chautauqua to the Ozark 

 dome. The Chautauqua connection existed only at the close of the De- 

 vonian. 



ELLIS ARCH (PRE-MI5SI3SIPPIAN) AND CENTRAL KANSAS 

 ARCH (POST MISSISSIPPIAN) 



NEMAHA 

 RANGE 



MILC3 



Feci 



BOURBON ARCH 



Fig. 5.13. Section along central Kansas arch, Nemaha Range, and Bourbon arch, taken from cross section 

 by Betty Kellett (1932). Line of cross section shown on map of Fig. 14.1. 



