28 LEE SAXD. 



change in tlie proportions of the pereentag'es on either 

 side of the maximum. 



It is evident that tlie finer grains, wliii li may have been 

 present originally or which may have been produced bj' 

 trituration afterwai'ds, are carried still farther awav. 

 Just how fa]' each different grade may be carried from the 

 place where it is fii'st taken up in the wind, has not been 

 made out satisfactorilj', but there can be no doubt that 

 the different grades in the fine material are let down at 

 successively greater distances according to their coarse- 

 ness. Some inferences with regard to these distances may 

 however be drawn ft'om the examination of some sedi- 

 ments, which the writer has taken occasion to collect 

 somewhat promiscuously. 



Four series of wind sediments have been taken from 

 successively more distant points in fi'ont of dunes and 

 sand drifts in Kansas, Illinois and North Dakota. The 

 analyses of these series show that the grains which 

 approximate nearest to the dune sand in size are not car- 

 ried very far. The samples from Rice county in Kansas 

 and those taken near Moline in Illinois exhibit merely a 

 decrease of the coarse admixtures and a corresponding 

 increase in the fine for increasing distances within a range 

 of two hundred feet (Tab. XYI and XVII). 



The maximum ingredient still consists of fine sand. 

 ^Yhile this rate of change is not very rapid, it is such as 

 to indicate that the maximum ingredient in the dr-ift sedi- 

 ments in this direction would change to very fine sand a 

 few hundred feet farther out. 



In distances less than tAvo himdred feet the percentage 

 of the fine ingredients increases from eight in the dune 



