THE GEE A T A M ERIC AN DESER T 211 



mile distant. Sometimes instead of the valleys being separated by a 

 range of round-topped hills this is accomplished by a continuous rounded 

 ridge. The sides of these hills are often very steep, making difficult the 

 direct passage over from one valley to another. 



In the regions of widest valleys the ranges of hills often show a suc- 

 cession of higher hills as one passes back from the valley to the highest 

 points on the divide, which may be from 300 to 400 feet above the level 

 of the valley. In the regions characterized by short valleys and basins 

 the general landscape is strikingly different because in such places the 

 hills rise on all sides without any regularity. Low hills, intermediate 

 hills and high hills are all closely associated, with no long separating 

 valleys. The result is a very abruptly rolling surface with rounded or 

 oblong depressions of varying depth, with the rounded or conical dunes 

 above. There are places where this sort of topography stretches in all 

 directions as far as one can see. 



As the name implies, the hills are composed of sand. This sand is 

 of a light straw color (not white) composed mostly of fine grained 

 quartz. The purest sand is found in the newest soil areas such as in 

 " blow-outs " or other places where the overlying vegetation has been 

 completely removed by the wind. In many places, notably on the river 

 flats and in the numerous thickets scattered throughout the hills, there 

 is a copious admixture of organic remains and so the surface soil in 

 such places is a rich black sandy loam and is very fertile. But the 

 characteristic soil of the region as a whole is the pure dune sand com- 

 posed of very fine particles. As to the chemical nature of the sand, the 

 following table shows it to be very high in insoluble mineral matter and 

 very low in soluble organic or inorganic plant-food materials. 



Composition of Sand Hill Soil ^ 



From Korest From Tops 



Nursery of Hills 



Insoluble matter 91.80 97.40 



Potash 0.14 0.05 



Soda 0.42 0.42 



Lime 0.38 0.12 



Iron oxide 0.01 0.01 



Alumina 2.76 0.84 



Phospliorus pentoxide 0.06 0.03 



Sulphur trioxide 0.19 0.21 



Water and organic matter 4.24 0.92 



Total roO.OO 100.00 



The following table shows the size of the soil particles in per cent., 

 and the average of three determinations from different stations in the 

 Sand Hills: 



* From a series of analyses by Dr. Samuel Avery, 1905. 



