ON THE SAND DUNES OF NORTHWESTERN INDIANA 251 



dates back to a distinct period in post-glacial history, and while 

 sand from one tract has been blown into the other belts, in places 

 obscuring the evidence of a beach, each tract is on the whole distinct. 



The exact locations of the shore lines have not been mapped in 

 the region involved, and in some places this will be impossible 

 because of the moving dunes; their approximate position, how- 

 ever, is as follows: Tolleston Beach passes through the southern 

 border of Miller and along the southern margin of Long Lake. 

 At Wicliffe it is doubtless north of the station on the electric line 

 and beginning with the eastern border of the broad opening through 

 the dunes at Wilson it is marked by the southern edge of the marsh 

 or muck tract within the main body of the dunes; this continues 

 almost to Michigan City. The Calumet Beach is just south of the 

 Little Calumet River in Lake County, and as far west as Wilson 

 where Lake Chicago had an extensive embayment. Beyond this 

 it parallels the South Shore Electric Railway as far as Johnsville, 

 being immediately south of it. The Glenwood Beach is south of 

 the Michigan Central Railroad in the eastern portion of Porter 

 County and after swinging south in a semicircle about the former 

 embayment, strikes west south of Hobart, some seven miles from 

 Lake Michigan. 



Due to the complex processes which have shaped the sand it is 

 difficult to make more than generalizations as to the rounding 

 and polishing of the grains, and shifting winds render it impossible 

 in some places to ascertain whether the sand at any given point 

 has recently arrived or is part of the original material of the dune. 

 Microscopic examination of the beach sand shows it dominantly sub- 

 angular. It is generally rather transparent and little pitted, the 

 corners frequently being sharp with little rounding. Back from 

 the beach the characteristic description would be subspherical, 

 many of the grains being well rounded and bean-shaped. All 

 sand which has been subjected to sand-blast action is pitted and 

 frosted, this being quite noticeable in the dune sand. Within 

 the older dune belts this gradation from the former shore line land- 

 ward is also apparent, but on account of the longer period of 

 exposure and consequent aeolian wear of all the sand, the contrast 

 between beach and dune sands is here less pronounced. 



