28 



Indiana University Studies 



up so the streams have been raised so that they will run off again. At 

 that point (just east of Ash Iron Springs) the sinking has been esti- 

 mated as not less than 100 feet. 



Turning again to the region of Blue River it is at once evident that 

 the region has not suffered the same depression as had occurred to the 

 west. On the contrary, the evidence is quite strong that the Blue River 

 region has recently been uplifted. 



Thus, it appears that Ashley explains the valley filling to 

 the west as due to depression, and at the same time gives facts 

 to show that farther east uplift has occurred. He further 

 states that the great width of the Ohio River valley below 

 Cannelton as compared to its gorge-like appearance above is 

 due to recent uplift to the eastward. 



Newsom,^ speaking especially in regards to the topography 

 of the Knobstone rocks in Washington County, has the follow- 

 ing to say: 



It will be noticed that these streams, after having cut through the 

 overlying limestones, have in all cases quickly cut down to their present 

 base levels of erosion, and that the main streams, especially Rush and 

 Delaney creeks, flow through flat-bottomed valleys. As their topog- 

 raphy indicates, these are silted up valleys in which the alluvial filling 

 is from 20 to 40 feet thick. 



This silting has been brought about by a depression of the land from 

 a former higher elevation, w^en the valleys w^ere eroded more deeply 

 than at present. With the depression of the surface the streams gradu- 

 ally became checked and the valleys filled. All of the main tributaries 

 of East White River in southern Indiana flow through valleys that have 

 been filled in this manner from 20 to 60 to 75 feet. 



Beede'' in summarizing the physiographic history of the 

 Bloomington Quadrangle, which lies immediately east of the 

 "American Bottoms" region, states that the present streams 

 flow at a level somewhat above the rock floors of their valleys 

 on account of depression following a period of erosion when 

 the stream valleys were trenched below their present floors. 

 Numerous citations from the publications of such students 

 of the Mississippi valley physiography as Glenn, Salisbury, 

 Hershey, and others might be made, in which valleys filled 

 with gravels, sands, and silts to depths of 100 to 150 feet or 

 more have been described, and this peculiarity explained as 

 due to the depression of the land. 



J. F. Newsom, Geologic Section Across Southern Indiana. 27th Annual Report of 

 the Department of Geology and Natural Resources. 1902. 



^ J. W. Beede, Features of Subterranean Drainage in the Bloomington Quadrangle. 

 Proceedings of the Indiana Academy of Science. 1910. 



