A SOUTHERN INDIANA GEOLOGICAL SECTION 25 I 



exposed in Indiana are the limestones and calcareous shales 

 of the Cincinnati group. Near Hanover these beds have an 

 exposed thickness of about 250 feet, reaching from near the 

 tops of the bluffs along the Ohio River down to and below the 

 level of that stream, which at this place is about 400 feet above 

 mean tide. Overlying this series of soft strata are hard lime- 

 stones belonging to the Clinton, Niagara, and Devonian (Cornif- 

 erous). The combined thickness of these beds is about 180 

 feet. 



The limestones resist the action of the weather, and owing 

 to these hard, resisting strata above, and the soft, easily eroded 

 strata below, the conditions are favorable to the formation of 

 bluffs and waterfalls. So it happens that each short stream that 

 flows eastward into the Ohio has the upper end of its gorge 

 marked by a precipice or waterfall, varying in height from 40 to 

 90 feet. 



When the top of the limestone is reached the country imme- 

 diately becomes approximately level. The Devonian limestone 

 is overlain by the Devonian black shale, and as this shale has no 

 hard beds immediately overlying it, it does not produce a rug- 

 ged topography. The dip of the Devonian limestone from Big 

 Spring, township 3 north 9 east, section 16 to section 20, 3 

 north 8 east is 231 feet, or a little over 33 feet to the mile. This 

 dip is not constant, but varies from 20 to 46 feet per mile, and 

 is in every respect sufficient to cause the westward flow of the 

 streams. 



In the eastern edge of Scott county the westward dip of the 

 Devonian limestone and the overlying Devonian black shale is 

 probably at its minimum ; the hills of this locality, and the 

 exposures of limestone in the valleys, are probably due to this 

 structural feature. While the hills are not high — ranging from 

 50 to 100 feet above the valleys — they nevertheless form the most 

 marked topographic feature between the Ohio River and the 

 Knobs. 



The Devonian limestone finally passes beneath the drainage 

 near the west line of township 8 east, the country immediately 



