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THE POPULAR SCIENCE MONTHLY 



is exposed to the wind, the blowing soil frequently prevents the growth 

 of field crops or any other plants. 



The flora of the dry valleys is very similar to that of the prairie 

 regions of the state, being especially rich in grasses. The principal 

 widely distributed plants of the dry valley are: switch grass (Panicum 

 virgatum) , wheat grass (Agropyrum pseudo-repens) , blue joint grass 

 {Calamagrostis canadensis), wild rye grass (Elymus canadensis), red 

 top (Agrostis alba), tickle grass (Agrostis hiemalis), rattlesnake grass 

 (Panicularia americana) , and a number of sedges (Carex tricliocarpa, 

 C. filiformis, etc.). All of these species are valuable forage plants and 

 they are all included in most of the hay that is put up from the valleys. 

 Besides these economic plants there are many other herbaceous members 

 of the prairie flora that have wandered into the Sand Hills and have 

 found congenial homes in these dry valleys. 



Fig. 12. The Rim of a Blow-out with the Fkixge of Roots 

 AND the Slipping Sands. 



The river flats properly belong to the dry valley type, since here we 

 find a soil free from surface water and with all of the above species of 

 plants often growing in profusion. These low flat areas extend from 

 the banks of the river back sometimes several hundred yards to the 

 bases of the hills. These flats or " benches " are well developed along 

 the Middle Loup Eiver. The river winds across the flats in a very 

 irregular course, sometimes cutting close to the hills on one side and 

 then shooting across to the hills on the opposite side of the flat. On 

 these flats and along the bank close to the stream occur the most of the 

 trees of the region. Thickets of plum {Prunus americana) , and cherry 



