874 The Scnid Hills of X(hr(isha 



soino ailniixturo of silt in tlii> liollows. No choinical analyses of the soils are 

 jjiven, l)ut deterniiiiations of liunius an<l nitroj^en for a few samples are quoteil 

 from another paper. 



The topography is irregularly undulating, with a local relief of 100 feet or 

 more in many jjlaces, and characterized by innumerable "choppy" hills and 

 basins, some of the latter occupied by lakes, ponds, or marshes. Small streams 

 are scarce, but there are a few rivers which have cut canyon-like valleys in the 

 sandstone. A very characteristic topographic feature is the "blow-out," formed 

 wherever breaks in the carpet of vegetation caused by fire or over-grazing allow 

 the wind to scoop out hollows in the sand, which may become 100 feet deep an<l 

 600 feet wide l)efore the vegetation regains a foothold. Outside of the blow-outs 

 there is no noticeable movement of the sand. 



The region is semi-arid, the average annual precipitation being about twenty 

 inches. The author says nothing of the seasonal distribution of rainfall, but 

 Plate 2 in TJ. S. Geol. Survey Water Supply Taper 234, 1909, shows that this 

 sand-hill country is in or near the only part of the United States which has over 

 80 per cent, of its rainfall in the six months April-September; from which it is 

 natural to conclude that there is some correlation between the extremely sandy 

 soil and the excess of summer rain, as has been pointed out by the reviewer for 

 some parts of the southeastern coastal plain. 



The country is essentially treeless, except along streams. The vegetation is 

 divided into about two dozen "associations," and the plants of each are listed, 

 mostly in alphabetical order, instead of in order of abundance, which would have 

 been much more significant. The most extensive type of vegetation is the ' ' bunch- 

 grass association," and the most abundant plant in it is the common grass 

 Andropofjon scoparius (called broom-sedge in the East). The vegetative cov- 

 ering, unlike that of dunes and deserts, is in most places dense enough for fire to 

 run through it at intervals; and this monograph is one of the very few ecological 

 papers that recognizes the importance of fire as an environmental factor, instead 

 of treating it as a mere accident and dismissing it in a few words. The author 

 says that many of the fires are started by lightning, a fact which some eeologists 

 who have studied prairie vegetation farther east seem loath to admit. 



Although little is said about the economic features, it is evident from the 

 illustrations that the area is very sparsely settled. (It had about two inhabitants 

 to the square mile in 1910, and sod-bouses are the most characteristic type of 

 architecture.) 



The bibliography, exclusive of cross-references, contains seventy-three titles, 

 some relating to the area studied and some merely of general interest. It would 

 have been appropriate to add the "Reconnoissance Survey of Western Nebras- 

 ka," by T. D. Rice and party, in FieJd Operations of the F. S. Bureau of Soils 

 for 1911 (pp. 187.5-1989, Plate 17), the separates of which were issued in June, 

 1913. Roland M. Harper. 



