369 
as outliers on the Mitchell. As indicated above, the Mitchell has been 
revealed by the stripping away of the over-lying clastic Chester materials 
by mechanical denudation. Outliers occur as much as ten miles east of 
the much dissected Chester scarp. The cross-section on the general map 
shows the topographic position and nature of the outliers. They are often 
ridge-like on the interstream tracts. 
Influence of Physiographic Development. 
Further explanation of the present topographic condition of the area 
may be gained from the interpretation of the topographic forms present in 
the region itself and in the adjacent regions. It appears that sometime 
about the middle of the Tertiary the entire region was reduced to a pene- 
plain, all parts having been reduced to their respective base-levels.” The 
region was then rejuvenated by uplift. Dissection of the uplifted peneplain 
followed. Dissection was fairly complete near the major streams, and in 
the regions of soft rocks local areas were reduced to base-level. These 
locally reduced plains indicate that the uplift amounted to something like 
175 feet. The region was again rejuvenated and dissection was renewed 
or continued. The Tertiary uplifted peneplain is now represented by rem- 
nants which are as much as 800 to 500 feet above the present base-level. 
The New Albany shale and the lower part of the Knobstone areas were 
reduced to a lowland in contrast to the region to the west of the Knobstone 
escarpment. The lowland plain consists of an undulating strip of country 
yarying from slightly above 400 feet in the lowlands adjacent the Ohio 
River to something like 600 feet in the low divide between Silver Creek 
and the tributaries of the Muscatatuck River. Since there are a large 
number of hills and rather flat interstream tracts at an elevation of 500 
feet or more at the south and coming up to 600 feet near the above men- 
tioned divide farther to the north, it has been stated that a _ base-level 
plain or local peneplain was formed at that level.° The writer concurs in 
the belief in a base-leveled plain of local area, and believes that its further 
development at the south was terminated by rejuvenation. The rejuvena- 
tion, however, was not necessarily brought about by uplift, as stated by 
Butts. The dissection of the plain was just as likely brought about by 
drainage changes made near the beginning of the Pleistocene. The present 
Ohio River is a large stream made up of a number of former drainage 
basins which were more or less individually destroyed or deranged by com- 
bination into a large major stream approximately skirting the outer limits 
of glacial advance. This drainage derangement took place largely near the 
beginning and during the earlier part of the Pleistocene. A very much 
5Kor the physiographic development of southern Indiana and associated regions 
see the following: C. A. Malott, the “‘“American Bottoms Region of Eastern Greene 
County, Indiana—A Type Unit in Southern Indiana Physiography, Ind. Univ. Studies 
No. 40, 1919, pp. 3-4, 21-86. Chas. Butts, Geology of Jefferson County, Kentucky, 
Kentucky Geological Survey, 1915, pp. 201-203. It may be stated here that valley 
filling is not a problem of the region considered in this paper. Such valley filling as 
occurs may be definitely referred to outwash and valley-train material from the 
Illinoian and Wisconsin glacial borders. 
tsa Butts, Geology of Jefferson County, Ky., Ky. Geological Survey, 1915, pp. 
