ON THE SAND DUNES OF NORTHWESTERN INDIANA 249 



running back from the lake and. at right angles to the trend of the 

 shore. On the assumption that all of the dune sands had been 

 blown inland from the present shore, it was anticipated that the 

 sand would show increasing signs of wear with increasing distance 

 from the shore. The microscope was used to determine the round- 

 ing of the grains, and for the gradations in size a tower of sieves 

 was found most satisfactory. The customary procedure in the 

 latter case was to weigh out 25 grams of sand and pass it through 

 sieves of 60, 80, and 100 mesh to the inch, thus giving four grades of 

 size, namely the sand retained in each screen and that passing 

 through the 100 mesh sieve. These groups were then weighed and 

 converted into percentages. 



The percentage of coarse sand was found to decline back from 

 the shore and there was a corresponding increase in the finer grades. 

 At a distance varying from one-fourth to one-half mile from the 

 beach, however, came a sharp increase in the proportion of coarse 

 sand along most of the lines on which samples were taken. The 

 change was quite regular, and reference to field notes showed that 

 on the lakeward side of the location for each sample which showed 

 the unexpected coarseness there was an area of muck or marsh. 

 Subsequent field investigations showed a more or less continuous 

 belt of this swamp or muck land between the dune belt nearest the 

 lake and the next one to the south, the dunes to the south being 

 lower and more rounded. Along the southern border of this flat 

 there were in places topographic suggestions of an old beach 

 ridge and from burrows of animals and holes which were dug, 

 very coarse sand was found. In the analyses of the samples from 

 the second dune belt, next south of the swamp belt, there was 

 again a progressive decrease in size of grain grading to the south. 

 The evidence, both topographic and petrographic, therefore points 

 to an old shore line, the dunes immediately to the south having been 

 built when the lake shore stood at its position, rather than having 

 been blown inland from the present beach. The muck or marsh 

 marks the approximate position of a former shore, and was perhaps 

 developed behind a barrier beach. 



The South Shore Electric Railway in the dune country runs 

 parallel to the lake and about a mile south of it. Most of the 

 dunes are north of the railroad but for much of the distance there 



