WIND DEPOSITS 679 



These localities it will be well to briefly describe, together with the sand 

 from each. 



On the north side of the Mississippi River, at JSTew Boston, in Illinois, 

 an ancient terrace is blown np into a sand ridge about a mile in length. 

 From all appearances the sand in these dunes has not yet traveled a half 

 mile. The materials in the original terrace are quit^ heterogeneous in 

 composition. The coarse grades have not yet had time to be entirely 

 left behind, but appear in a small quantity in some of the dune sand. 

 One of the samples was taken by skimming the surface on the crest of a 

 ripple. This is unique among all the analyses of typical dune sand in 

 having medium sand as its maximum ingredient. Had it been taken a 

 little deeper it would have been more like the rest, for the coarser grains 

 are least easily dislodged from this exposed position and remain, while 

 the finer sand is blown away. Some coarse dust is still mixed in the 

 sand at this place in one instance. All taken together and compared 

 with sand from other places, these samples may be said to be imperfectly 

 sorted, owing no doubt to the recency of the inception of the wind action 

 in this locality. 



The dunes on the southeast shore of Lake Michigan have furnished 

 the materials for six analyses. These sand hills have been recently 

 formed, and are largely made up of sand that is freshly supplied by 

 present wave action on the shore of the lake. In this place also the 

 coarse grades occur with the typical dune sand in small quantities on 

 the very top and front slope of the hills; but there is practically no 

 coarse dust to be seen, presumably because no such fine material is pres- 

 ent in the beach sand. This locality and the previous are the only ones 

 that furnish instances of dune sand having a secondary maximum in 

 the coarser grades. 



The bluffs facing the bottom lands of the Mississippi east of Cordova, 

 in Illinois, are here and there being drifted by the northwest winds. 

 Some sand taken from a small drift only a foot in height exhibits im- 

 perfect sorting like that observed in the sand from New Boston and 

 Michigan City. 



In Rice County, in the central part of Kansas, there is a tract of sand 

 hills extending many miles along the Little Arkansas River. These are 

 derived from underlying late Tertiary beds. Their extensive develop- 

 ment shows that the wind has been at work here for some considerable 

 time. The sand is correspondingly uniform and rock fragments of 

 either extreme size are absent. One of the analyses exhibits the mechan- 

 ical composition of a single thin lamina in the dune, evidently laid down 

 under a uniform wind velocity. It is interesting as indicating, when 



