WISCONSIN DBIFT BOEDER. 



85 



the Wisconsin invasion. They are light but cover a convex surface which was polished smoothly. 

 The table below includes all recorded observations near the limits of the Wisconsin drift in 

 Indiana, whether of the Wisconsin or earlier glaciation. 



Glacial slriiv in Indiana. 



Quarry 3 miles southeast of Kentland . 



In same quarry 



Monon 



Rensselaer 



Rainsville 



2 miles east of Williamsport . 

 Williamsport 



Near Darlington (3 occurrences). 



D,i 



Sec. 20, T. 15 N., R. 5 W 



Sec. 27, T. 15N..R. 6 W 



Sec. 1,T.15N 5 E.7W 



Sec. 21, T. 16N.,R. 7W 



Sec. 24, T. 16N.,R.7W 



Sec. 25, T. 16N..R. 7 W 



Railroad cut near Maple Grove. 



Greencastle 



Greeneastle, southwestern part. 



Do. 



[ All observations have magnetic bearing except those of Coulter, which are corrected to the true meridian. 



b From Lake Michigan lobe? 



GLACIAL DRAINAGE. 



Traces of drainage systems which depart somewhat from the present systems are found in 

 the eastern part of the border district. The principal headwater branch of East White River, 

 locally called Blue River, and Flat Rock Creek, the stream next in importance, utilize part of 

 a complex system of valleys which cut the country they traverse into large island-like tracts. 

 This network of channels appears to have been developed on flat plains in which preglacial 

 drainage lines had been obliterated and new lines had to be opened upon the retreat of the 

 ice sheet. The channels mark the rambling courses taken by streams before they had become 

 established in the present lines. 



Some of the peculiarities of drainage displayed by Flat Rock Creek were noted and dis- 

 cussed some years since by C. S. Beachler. 1 The branching channels and the several islands 

 inclosed by them were noted and their boundaries mapped approximately by Collett in his 

 report on Shelby County. 2 They were interpreted to be the lines of discharge of streams which 

 had their source in the retreating ice sheet. Collett called attention to the presence of gravel 

 and sand to a depth of about 35 feet below the broad bottoms of this system of branching 

 channels and interpreted these deposits to be due to a grading up or partial refilling of the chan- 

 nels by the outwash from the ice sheet. 



The grading up which the valleys experienced implies a large amount of preceding erosion. 

 The removal of this gravel filling would give the valleys a depth of 50 to 75 feet or more and a 

 combined width of 2 to 6 miles in their course through Shelby and Bartholomew counties. 

 Notwithstanding the fact that this wide cutting has been done not in rock but in glacial deposits 

 its amount appears very great to have been effected in connection with the recession of the ice 

 in the Wisconshi stage. It seems more nearly in harmony with post-Illinoian erosion. 



An examination of the bluffs of these valleys and of the tracts inclosed by the branching 

 channels shows that the general level of the surface of the older or Illinoian drift is higher than 

 the gravel filling in the valleys for at least as far up the valleys as the vicinity of Shelbyville if 



1 An abandoned Pleistocene river channel in eastern Indiana: Jour. Geology, vol. 2, 1S94, pp. 62-65. 

 1 Eleventh Ann. Rept. Indiana Dept. Geology and Nat. Hist., 18S1, map opposite p. 55. 



