869 



icll. As iiidic'ilcil al.dvc. Ilic .Milclicll liiis been 

 : ii\v;iy (if tlir (i\ci-l.\ iiiii chistic ChcstiT materials 

 liy iiiccliMiiic.-il (It'iiiidiilidii. (Mitlicrs ncciir ;is iiiucli ;is ten miles east of 

 the iimcli (lisscH'ted Chester sc-ii]). The cidss-scctioM on the general map 

 shows the topogi'apliie iMisitioii :iii(l nature of tiic outliers. They are often 

 rid.iie-like on the iiiterstr(>inn tracts. 



I iifliitiirr of rinisiiKini i)}nc lt( rcldiinniil . 



Fiirthei- exi.lauatioii of the present toiio},'rapliic condition of the area 

 may lie j^aiiied from tiie inteiiiretation of tiie toi>ouraphi(' foi'iiis present in 

 the rcfjion itself and in tlie ad.jacent rejiioiis. It appears that sometime 

 about the middle of tiie Teitiaiy the entire re;:ion was reduced to a pene- 

 lilaiii, iill i)arts havini; lieen reduced to their respective base-levels.'' The 

 rcuiou was then rejuvenated by uplift. Dissection of the uplifted iK^neplain 

 followed. Dissection was fairly complete lu'ar the major streams, and in 

 the regions of soft rocks local areas were reduced to base-level. These 

 locally reduced i>lains indicate that the uplift amounted to something like 

 175 feet. The region w-as again rejuvenated and dissection was renewed 

 or continued. The Tertiary uplifted peneplain is now repre.sented by rem- 

 nants which are as much as :!(»() t<i ."ioo feet above the present base-level. 



The New Albany shale and th(> lower part of the Knobstone areas were 

 reduced to a lowland in contrast to the region to the west of the Knohstcme 

 escarpment. The lowland plain consists of an undulating strip of country 

 varying from slightly above 400 feet in the lowlands adjacent the Ohio 

 liiver to .something like (KM) feet in the low divide lietween Silver Creek 

 and the tributaries of the Muscatatuck Kiver. Since there are a large 

 number of hills and rather flat interstream tracts at an elevation of oOO 

 feet or more at the south and coming up to GOO feet near the ahove 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 nplift. 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 WQve 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 earliei' jiart of the Pleistocene.* A very much 



■"For the physiographic (li'vi'loiiintnt of siiuiliiTii Indiana and associated regions 

 sfo till' following: C. A. Malott, the '•Aiiicricjiii Hottoms Region of Eastern Gteene 

 ("oiiiitv. Indiana — A Type Unit in Soutlierii Iiidl;iiia Phvsiotrraphv, Iiid. I'niv. Studies 

 Xo. 4(1. till!), pp. S-4, 21-S6. Chas. Butts, (icology of .Icff.rson County. Keiitu.'ky. 

 Kentucky (ieologieal Survey. 1915, pp. 201-lio:!. It may l)e stated here that valley 

 filling is not a prol)leni of the region considered in this paper. Such valley filling as 

 occurs may be definitely referred to outwash and valley-train material from the 

 Illinoiau and Wisconsin glacial tjorders. 



'■('has. Butts, Geology of Jefferson County. Ky.. Ky. Geological Survey, 191.", pp. 

 201-20:1. 



