A SOUTHERN INDIANA GEOLOGICAL SECTION 255 



by the coal-bearing shales and sandstones of the Upper Carbon- 

 iferous. These beds are easily attacked by eroding agencies, 

 and have, therefore, already been worn down very near to their 

 base level of erosion (if, indeed, they have ever been high above 

 that level), leaving a comparatively level flat country. This 

 region is covered with more or less glacial material. 



The accompanying profile section shows clearly these differ- 

 ent topographic features, and also the relations between the 

 topography and the underlying strata. 



CONCLUSION. 



In conclusion, attention should be called to the following 

 points : 



a. In passing from east to west across southern Indiana, three 

 prominent topographic features are crossed, and these features 

 are the results of combinations of strata as follows: (1) the high 

 eastward escarpment along the Ohio River caused by a thick 

 series of easily eroded calcareous shales overlain by thick and 

 resisting limestones ; (2) the high eastward-facing escarpment 

 with its outliers to the east, known as the " Knobs." This escarp- 

 ment is the result of a thick series of soft clay and sandy shales, 

 protected by sandstones and resisting limestones. Along the line 

 under discussion this escarpment is twentj-eight miles west of 

 the escarpment along the Ohio; (3) the high hills of Martin 

 county, which are the result of a series of limestones and sand- 

 stones capped by more resisting sandstones and which do not 

 rise as an escarpment from the east, but become gradually higher, 

 owing to the resisting nature of their lowest beds. The distance 

 from the Knobstone escarpment to the highest hills capped with 

 the Mansfield sandstone is about thirty miles. 



b. The structure of each of these topographic features where 

 crossed by the section is essentially the same in different stages 

 of development, i. e., that of a dissected plateau, sloping gently 

 to the west. In the eastern, or the Devonian limestone plateau, 

 in the region of Ohio, dissection has scarcely begun, as none 

 except the streams flowing directly into the Ohio have deep 



