256 JOHN F. NEWSOM 



gorges, and these are only from one-half to one and a half miles 

 long ; in the middle, or Knobstone plateau, dissection has pro- 

 gressed much further than in the eastern one ; while the western 

 or Mansfield sandstone plateau has been completely dissected 

 by its streams. 



It is possible that this peculiarity in the amount of erosion 

 that has taken place in these different plateaus is the result of 

 the character and former upward extension of the overlying 

 formations in each case. 



c. The top of the eastern plateau where crossed by the sec- 

 tion is 800 feet above the sea, that of the middle is 820 feet, and 

 that of the western 880 feet above tide, while but a short distance 

 to the north or south the topographic sheets show the elevations 

 of these plateaus to correspond even more closely. 



These closely corresponding elevations point strongly to the 

 conclusion that the present topography of southern Indiana has 

 developed from an old base level ; a former plain of deposition, 

 or a combination of the two, might, however, have given rise to 

 the present conditions. 



John F. Newsom. 



Indiana University, 



Bloomington, Indiana. 



