252 Proceedings of Indiana Academy of Science. 



is sharply trenched by minor stream development. The npland spaces 

 between the minor stream valleys are rather gently rolling or flat, with 

 some development of shallow sinkhole topography. 



Geologic Conditiom and PhymograpJiic Development of the Locality. — 

 Since an miderstanding of the geology of a locality is frequently quite essen- 

 tial in the interpretation of the topographic forms present a brief sketch 

 of the geology will be given here. The upland mass is comix>sed chiefly 

 of solidified Mississippian rocks of Keokuk and Warsaw age, covered over 

 with a thin soil mantle except where the slopes are quite steep. Small 

 deposits of late Tertiary gravel are present on the upland adjacent to 

 Salt Creek valley. Salt Creek valley is partly Idled with Pleistocene 

 and recent alluvial material. 



The rocks of Keokuk age are massive to thin bedded iniimre sandstones 

 and sandy shales, all usually of a bluish color, consisting of the upper 

 part of the so-called Knobstone group of rocks. These sandy shales and 

 argillaceous, fine-grained sandstones are mainly exposed on the steep 

 slopes of the area. More than 200 feet of the Knobstone rocks are ex- 

 posed on the steep sloi^es on the eastern side . of the area. Everywhere 

 on top of the upland the clastic Knobstone rocks are covered with the 

 thin to massive bedded Harrodsburg limestone of Warsaw age. The con- 

 tact of this limestone with the Tinderlying Knobstone is about 740 above 

 sea level at the east side of the area, about 650 feet in the middle of the 

 area, and about 580 feet in the hill east of the mouth of Clear Creek near 

 the southwest corner of the area. With these figures in mind, reference 

 to the topographic map will show that practically all of the tillable upland 

 is on the Harrodsburg limestone. This limestone has a total thickness of 

 about 90 feet, but only in one or two localities in the mapped area is the 

 total thickness to be found. This limestone area is covered by a red soil 

 in and on which are quantities of chert which has weathered from the 

 limestone. 



The dip of the Mississippian rocks may be computed from the figures 

 given above on the contact of the Harrodsburg limestone and the Knob- 

 stone rocks. The dip is mainly west, or slightly south of west. The rate 

 of dip is variable, being abnormally great in the eastern half of the area. 

 There, the dip amounts to something like 80 feet to the mile, while in the 

 western half of the area the dip has subsided to approximately the normal 

 amount of 35 feet to the mile. The extraordinary dip at the eastern side 

 of the area is probably because of proximity to a considerable structural 

 disturbance a short distance east of the mapped area. 



The region is a dissected plain. The topographic map shows distinctly 

 the general level of the plain in the gently rolling to flat upland inter- 

 stream spaces. This upland plain is about 7G0 feet above sea level at the 

 eastern side of the area. It inclines to the west where it has an elevation 

 of about G75 feet. This plain as preserved in the area is a portion of a 

 more extensive one developed on the rather resistant Harrodsburg lime- 

 stone which caps the upland area. The Harrodsburg limestone capping 

 has protected the underlying easily eroded and weathered Knobstone rocks. 

 Since this partly preserved plain' inclines practically with the dip of the 

 Harrodsburg limestone upon which it is developed, it may be regarded as 

 a structural plain. It may al.so be called a structural peneplain, since it is 



