252 Proceedings of Indiana Academy of Science. 
is sharply trenched by minor stream development. The upland spaces 
between the minor stream valleys are rather gently rolling or flat, with 
some development of shallow sinkhole topography. 
Geologic Conditions and Physiographic Development of the Locality— 
Since an understanding 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 composed 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 filled with Pleistocene 
and recent alluvial material. 
The rocks of Keokuk age are massive to thin bedded impure 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 slopes 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 underlying 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 55 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 760 feet above sea level at the 
eastern side of the area. It inclines to the west where it has an elevation 
of about 675 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 also be called a structural peneplain, since it is 
