WIND DEPOSITS 681 



their topographic features these hills resemble sand dunes, but the activ- 

 ity of the winds seems to have come to a standstill at present except in 

 a few places on the summits of the ridges. Two samples from this lo- 

 cality show a remarkably perfect sorting, though one of them, which was 

 taken from a drifting cultivated field, carries the usual quantity of fine 

 grades present in blo\\Ti soils. 



It will be noticed that in all these samples of dune sand, excepting 

 the one collected by skimming the ridge of a ripple, the maximum in- 

 gredient is fine sand. In one instance 92 per cent consists of this grade, 

 while in three cases it forms over 80 per cent of the bulk. Where lowest 

 it forms 45 per cent, and it averages 65 per cent in all the sand exam- 

 ined. In three of the samples 90 per cent is distributed among four 

 grades; in 22 among three grades, and in 13 between only two. Here 

 also the admixtures arrange themselves in two series, decreasing on 

 either side of the maximum. The coarse admixtures form a less rapidly 

 decreasing series than the fine, the former extending over five grades in 

 the general average and the latter over onty three grades. The extension 

 of either is evidently diminished by prolonged wind action, which results 

 in more perfect elimination of grains near either extreme. 



List of Samples in TaMe 23 



211. Rear slope of ripples in dune sand, New Boston, Illinois. 



212. Dune sand, New Boston, Illinois. 



213. Top of ripple on dune sand, New Boston, Illinois. 



214. Front slope of dune. New Boston, Illinois. 



215. Upper rear slope of a dune, Michigan City, Indiana. 



216. Dune sand, Michigan City,~ Indiana. 



217. Typical dune sand, Michigan City, Indiana. 



218. Near the crest of a dune, Michigan City, Indiana. 



219. From the crest of a dune, Michigan City, Indiana. 



220. From the top of a dune, Michigan City, Indiana. 



221. Blown sand from the river bluffs, Cordova, Illinois. 



222. From the front slope of a dune, Rice County, Kansas, 



223. From the rear slope of a dune. Rice County, Kansas. 



224. From a single seam in the front slope of a dune. Rice County, Kansas. 



225. Dune sand. Folly's Cove, Massachusetts. 



226. Dune sand. Folly's Cove, Massachusetts. 



227. Blown sand in a field, Barnes County, North Dakota. 



228. Blown sand in a field, Cooperstown, Griggs County, North Dakota. 



229. Blown sand in a field, Steele County, North Dakota. 



230. Blown sand, Steele County, North Dakota. 



231. Blown sand, Griggs County, North Dakota. 



232. Dune sand, Tampico, Illinois. 



233. Dune sand, Hooppole, Illinois. 



234. Blown sand, Lindsborg, Kansas, 



