A SOUTHERN INDIANA GEOLOGICAL SECTION 2 S3 



very gently to the west, and with outliers to the east. The geo- 

 logical conditions, so far as they bear upon topography, are very 

 similar to those along the Ohio River, to the east, i. e., a thick 

 series of soft and unresisting strata is capped by sandstone and 

 more resisting limestones, thus making possible bold hills and 

 steep slopes. 



The parting between the Knobstone and the overlying lime- 

 stone is not a sharp one, but is made up of interstratified limy 

 and sandy layers, indicating a gradual change in the conditions 

 of sedimentation. The easternmost point in the line of parting 

 between the Knobstone group and the overlying limestone is at 

 the southeast corner of section 18, 3 north 5 east. Passing on 

 westward the top of the Knobstone is found lower and lower in 

 the hills, until it finally passes beneath the drainage in the north- 

 east quarter of section 19, 3 north 3 east, at an elevation of 537 

 feet, or 342 feet lower than its outcrop, just eleven and one-half 

 miles east. This shows a general westward dip averaging about 

 twenty-six feet per mile. 



The sink hole region.- — Overlying the Knobstone group, and 

 still dipping to the west are the Harrodsburg and Mitchell lime- 

 stones (of Hopkins and Siebenthal) , and the Kaskaskia group, 

 all belonging to the Lower Carboniferous. In the region of its 

 easternmost exposure the limestone is very thin, being eroded to 

 a feather edge. Passing westward from its easternmost expos- 

 ure, it is found lower and lower in the hills, because of its west- 

 ward dip, and the country becomes accordingly less rugged and 

 takes on the gently rolling and pitted sink hole character com- 

 mon in limestone regions. 



In this region and on westward across the outcropping Mit- 

 chell limestones, and until the Kaskaskia beds are reached, the 

 country has a very gentle westward slope. This is less, however, 

 than is to be found east of the " Knobs," and it is also less than 

 the dip of the rocks ; this is due to the fact that the limestones 

 do not weather so easily as do the shales. 



There is a noticeable increase in the size of the sink holes in 

 going across the limestone region from east to west. The sink 



