BORDEK OF THE ILLINOIAN DRIFT. 255 



and carries also a few low sM^ells. There was probably considerable obstruc- 

 tion, if not a complete damming, of the lower course of Beanblossom Creek 

 by the portion of the ice sheet immediately west of the reentrant angle. 

 Such an obstruction is suggested not only by the fact that the lower course 

 of the creek enters the drift-covered region but also by the features in the 

 part of the valley just below the drift ridge at Needmore. Only an occa- 

 sional pebble appears below the ridge to testify to transportation of glacial 

 material down the valley. 



South from Beanblossom Creek considerable till is banked against the 

 slope, but the dividing ridge carries only bowlders and occasional thin 

 deposits of till. The bowlders, as noted above, have apparently been 

 rolled down ravines south of the divide to some distance beyond the ice 

 margin. 



In Salt Creek Valley the drift border connects with a glacial ten-ace 

 that leads down the valley beyond the limits of Brown County. Where 

 uneroded this terrace stands fully 50 feet above the present stream. The 

 valley of Salt Creek seems to have been the main line of discharge for 

 glacial waters in the elevated region. The drift deposits at the place where 

 the ice margin crossed the valley are not so conspicuous as on Beanblossom 

 Creek, probably because so large an amount was carried down Salt Creek 

 Valley during their deposition. 



On the elevated uplands in eastern Brown County the drift is in places 

 40 feet thick, but it is usually a thin deposit, scarcely sufficient to form a 

 continuous di-ift sheet. There appears to have been some outwash into 

 Middle Salt Creek, for gold, supposed to be of glacial derivation, is reported 

 to occur in the alluvium at Elkinsville,^ but it was a less important line of 

 discharge than the North or main Salt Creek Valley. 



On the low plain in Jackson County a prominent drift ridge, known 

 as "Chestnut Ridge," stands near the glacial boundary. It is not at the 

 extreme limits of the di-ift, there being' a plain west of it a few miles in 

 width which is underlain by clay and sand carrying glacial pebbles. It 

 should, however, be considered in connection with the drift border, since it 

 is not unlikely that the ice sheet formed this ridge while it was still occupy- 

 ing neighboring' parts of the drift border. 



^ Eept. Geol. Survey Indiana, 1874, p. 107. 



