PldiKifion ^Iranii Piriir-i/. 2.":! 



;i plain devolopod on tlu> slriicliii-al level of tin* IIarro(lshnr« limestone iiy 

 Ihivial a.i,'encies. It owes its lU'eservation as a plain to tlio rather superini- 

 resistance of the limestone Id mechanical denudation, and to the fact that 

 its snhterranean drainage in llie limestone has temporarily greatly retarded 

 lis tluvial destruction. Where the streams have cut through the Harnids- 

 liiiri,' limestone into the mechanically non-resistant Knohstone rocks tliey 

 are flanked by very steep slopes, having angles of 20 to HO degrees from 

 the horizontal. This sliaip stream trenching is Muite characteristic of 

 Knohstone topography. 



The structural plain developed on the Harrodshurg limestone extends 

 miles eastward from th(> area, and rises directly with the strata in that 

 direction. But less and less of the interstream surface is level to tlie east- 

 ward; and tinally the Harrodshurg limestone ceases to be present, though 

 the plain itself has risen l<i an elevation (tf 1)00 to 1.000 feet above sea 

 level. The divides in this lii.uli-lc\cl area are rather sharp, but have even 

 crests of approximately the s:niie elevation. This area furnislies a most 

 excellent example of mature Iop<igrai)hy. This maturely dissected area 

 which reaches elevations of iiod to l.ooo feel above sea level is probably 

 representative of the earlier Tertiary tluvial i>eneplain, and may be cor- 

 related with the Highland Kim pene])lain of Kentucky and Tennessee. The 

 Highland Kim iieneplain renniants represent the highest level attaine:! 

 in Indiana. In the region in question no part of the area reaches up to 

 the Highland Rim level. P<utious 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 

 elevations on the upland a<l.jacent to the valley of Salt Creek is evidence 

 of local peneplanation. These gravels were noticed near the higher place-; 

 on the ridge in section 34. l)etween Salt Creek and Lower Cut-olf 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 valley 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 -10 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 which 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 Xamr of Cut-Off I'iracii. I'pper 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 



