THE SAND-HILL EEGION. 11 



plete, and there is no surface run-off. The hills are comparatively 

 high and rise from 60 to 100 feet above the interior valleys and from 

 200 to 300 feet above the valleys of the main streams, such as the 

 Middle Loup. Along such streams permanent springs are more or 

 less common, which indicates that an impervious substratum under- 

 hes the hills at no great depth. It is with these choppy hills that the 

 forester is principally concerned, since they have no agricultural value 

 whatever. They are evidently the youngest of the hills and have not 

 yet ceased to be affected by the wind, though there is evidence that 

 they have become a good deal more stable since the buffalo ceased to 

 trample them. With overgrazing or any other influence which kills 

 the vegetation the sand is released, ''blow-outs" are formed, and in 

 a few years a hilltop may change position appreciably. Since these 

 least stable hills are so near to the agricultural land of eastern Nebraska 

 their fixation is of great importance. 



While the dune sand of the hilltops, as shown by analysis of the 

 soil at Halsey, is practically pure silica ^ and contains less than 1 per 

 cent of organic matter, the soil of the valleys and pockets is usually 

 very rich in humus. The continuous collection of this material is 

 made possible by the lack of surface drainage. As a result of it the 

 vegetation of the bottoms is very heavy, while that of the hilltops is 

 correspondingly light. The heavy vegetation of the bottoms uses 

 up a lot of the moisture, and this, in the absence of rains, makes 

 these by all odds the most difficult sites for the introduction of new 

 plant life. 



CLIMATE. 



PRECIPITATION. 



The rainfall of the sand-hill region varies from 15 to 26 inches per 

 annum. It is well distributed to assist the ordinary forms of vegeta- 

 tion, since it comes largely in the growing season, but because of the 

 decided lack of snow young woody plants which need protection in 

 their first years have great difficulty in getting started. 



The precipitation increases month by month from the beginning 

 to the middle of the year and then decreases to the end of the year. 

 Since May and June are moist, coniferous-tree growth seems to be 

 especially favored. The dryness of the fall months permits proper 

 ripening of woody growth, so that fall frosts seldom do any harm. 



Table 1 shows the precipitation at Halsey, Nebr., and Garden City, 

 Kans., headquarters of the Nebraska and Kansas Forests, respec- 

 tively. For comparison with a yellow-pine region the records for 

 Fort Robinson, Nebr., are also given. 



1 Analysis of soil from hilltop at Halsey Nursery showed 97.4 per cent of insoluble mineral matter. 



