Planation Stream Piracy. 253 
a plain developed on the structural level of the Harrodsburg limestone by 
fluvial agencies. It owes its preservation as a plain to the rather superior 
resistance of the limestone to mechanical denudation, and to the fact that 
its subterranean drainage in the limestone has temporarily greatly retarded 
its fluvial destruction. Where the streams have cut through the Harrods- 
burg limestone into the mechanically non-resistant Knobstone rocks they 
are flanked by very steep slopes, having angles of 20 to 50 degrees from 
the horizontal. This sharp stream trenching is quite characteristic of 
Kknobstone topography. 
The structural plain developed on the Harrodsburg limestone extends 
miles eastward from the area, and rises directly with the strata in that 
direction. But less and less of the interstream surface is level to the east- 
ward; and finally the Harrodsburg limestone ceases to be present, though 
the plain itself has risen to an elevation of 900 to 1,000 feet above sea 
level, The divides in this high-level area are rather sharp, but haye even 
crests of approximately the same elevation. This area furnishes a most 
excellent example of mature topography. This maturely dissected area 
which reaches elevations of 900 to 1,000 feet above sea level is probably 
representative of the earlier Tertiary fluvial peneplain, and may be cor- 
related with the Highland Rim peneplain of Kentucky and Tennessee. The 
Highland Rim peneplain remnants represent the highest level attained 
in Indiana. In the region in question no part of the area reaches up to 
the Highland Rim level. Portions of the structural plain, however, probably 
represent a later more local peneplain of fluvial origin. This level has an 
elevation of 650 to 700 feet. The presence of old stream gravels at these 
eleyations on the upland adjacent to the valley of Salt Creek is evidence 
of local peneplanation. These gravels were noticed near the higher places 
on the ridge in section 34, between Salt Creek and Lower Cut-off Creek. 
They are probably of latest Tertiary age, having been deposited as alluvial 
gravels previous to the uplift which is ordinarily believed to have ushered 
in the Pleistocene. 
The Pleistocene uplift was responsible for the stream trenching of the 
area. This uplift allowed Salt Creek to intrench itself into the uplifted 
land mass 150 feet or more below the stream gravels of late Tertiary age 
Stream trenching was considerably greater than the difference in the eleva- 
tion of the present graded valley and the old gravels, since the present 
valley is partially filled with Pleistocene gravels, sands, and silts. It is 
filled some 50 to 80 feet below the present stream level. The upper part of 
the Pleistocene yalley filling has been partly removed and reworked by the 
meandering stream over the over-broadened valley-flat. Terraces ranging 
in height from a few feet to over 40 feet above the present flood plain indi- 
cate that the Pleistocene filling of the intrenchesd valley has been partly 
removed. This Pleistocene valley material is composed largely of material 
derived from the rocks in whick the valley is cut. but a portion of it is dis- 
tinctly outwash material from the Illinois glacial lobe which came as far 
south as the headwaters of Salt Creek at the northern and northeastern 
limits of the triangular-shaped unglacial area in southern Indiana. 
The Name of Cut-Off Piracy._—Upper and Lower Cut-off creeks are two 
small streams shown on the map accompanying this paper, and the names 
are applied to the streams for the first time, in this paper. These names 
