QUATERNARY AGE. 299 



Some eminent geologists have sought to account for these hills 

 by the theory that the winds in the course of ages have blown the 

 sand from the bars on the rivers until their accumulation caused 

 these peculiar elevations. There are many difficulties in the way 

 of this theory. East of Columbus no sand-hills are found, and it is 

 hard to conceive how they should come to be limited to the west- 

 ern portion of the State if they were formed in this way. In some 

 places at least the hills are partly composed of large pebbles and 

 stones that could not have been moved by the winds. This is espe- 

 cially the case in some of these hills south and east of Kenesaw, in 

 Adams County. I suggest, as a provisional explanation, the prob- 

 ability that, south of the Platte, the lines of sand-hills show the 

 track of a current in the old lake that produced the Loess deposits. 

 It is well known that fine sediment is deposited in still water, but 

 coarse materials, such as sand and pebbles, in the borders and in 

 tracks of currents. As the whole country rises toward the west, 

 the water here may have veen very rapid, and the land in process 

 of drying up when it was yet deep at its lower levels. Both 

 causes, the currents and the winds, may have co-operated to pro- 

 duce these deposits. I am also satisfied that in some localities the 

 sand-hills are nothing more than modified Loess deposits. They 

 are Loess deposits, with all the alumina, organic matter ard finest 

 sand washed out of them. This at least seems to be the origin of 

 some of the sand-hills on the Lower Loup, where they occupy a 

 lower level than the Loess deposits. These two deposits so often 

 shade into each other in the vicinity of the sand-hills, rendering it 

 impossible to tell where the one begins and the other ends, that the 

 theory of their common origin best explains the phenomena of 

 these formations. After the western portion of the Loess deposits 

 first became dry land, water-agencies were yet so powerful espec- 

 ially in flood times that much of it must have been re modified, and 

 the coarser materials left to form sand-hills. And as we have 

 already seen in another chapter, some of,the sand and gravel hills 

 partake largely of the Old \Vorld Kames, and may have been 

 formed in the same way, especially as against these the Loess de- 

 posits abut. The sand-hills on the Upper Loup and the Niobrara 

 probably derived the bulk of their materials directly from the Plio- 

 cene Tertiary deposits, which were mainly loosely compacted 

 sands. This old Pliocene lake was probably perpetuated here 

 down through Loess times to the borders of our own era. Even 



