.-in avt'r;ij;e tlik-kiK'.s.s of iicrliiips loss lliaii lU i'vvl. Tlu- .Mitchell liiiicstoiic 

 is ji group of liinestoiios totaling soiuo 10)0 foot in thioknoss in tiio region. 

 It consists of about 220 feet of St. Louis limestone at tlio bottom, about 90 

 foot of Fredonia Oolite (representing the St. Genievieve). and about 4U 

 foot of Gasper Oolite (distinctly of Chester age) at the top. The Mitchell 

 limestone, though composed of several geologic units, is really a great 

 lithologic unit of compact, thin-bedded, highly jointed limestone layers with 

 occasional thin bands of shale and impure limestone horizons. The lime- 

 stone in places contains considerable chert. Near the top of the St. Louis 

 chort is (juite conspicuous and boars numerous colonies of the coral Litho- 

 ■strotioii canadcHiiC. The uppermost strata outcropping in the region are the 

 clastic members of the Chester series above the Mitchell limestone. The 

 sandstones and sliales, however, contain one or more members of limestone. 

 The total thickness in the region is Mpi)roximately 200 feet. 



Regional Dip. 



The above lithologic series dip to the west or probably a little soutli of 

 west at the north of tlie area, at the rate of about oO feet to the mile. Local 

 dips may be much more or less than this amount, due to anticlinal or terrace 

 flexures, such as the geologic cross-section shows. This regional dip causes 

 each lithological unit to outcrop along its strike extending almost north 

 and south. The lowest unit outcrops farthest east and the others follow 

 in order to the west. No particular unit has an areal outcrop proix)rtional 

 in width to its thickness with respect to any other unit. This is because of 

 the difference in resistance of the units and the topographic condition. The 

 topographic condition of the area occasionally allows a thinner unit to 

 occupy a wide area while a thicker unit may have a relatively imrrow 

 outcrop. 



Arval Outcrop of LitlioJogic Units. 



For the details of the areal outcrop of the above geologic or lithologic 

 units, reference must be made to a geologic map. It may be stated here 

 parenthetically that the writer is firmly convinced that no detailed phy- 

 siographic study of the driftless area of southern Indiana can be adequately 

 made without tlio aid of detailed lithologic knowledge of the region. This is 

 essentially a geologic study, and its expression is found in the geologic map 

 and the stratigraphic column. A general idea of the representative outcrop 

 may be gained by reference to the geologic and topographic cross-section 

 on the general map. This map also shows the position of Knobstone escarp- 

 ment by means f>f hachure lines, following Xewsom's map.' This escarpment 

 is composed of the Knobstone strata. The lowland area to the east consists 

 of both the lower softer portion of the Knobstone strata and the unresistant 

 Now Albany shale. At the south the Mississippian limestone belt be^ns 

 at the very top of the escarpment and extends westward. In the middle por- 

 tion of the area only the Harrodsburg limestone extends as far east as the 



ij. F. Newsom, A Geologic and Topographic Section Across Soiitliorn Indiana. 

 >6th Annual Report, Ind. Dept. of Geol. and Natural Res. 1901. 



