of large size was observed in which all four parts were present with- 

 out any apparent modification. Deviations from the nonnal may usu- 

 ally be referred to three general causes : ( i ) the blowout is young 

 and not all the parts are developed (PI. VI, Fig. i ; PI. VII, Fig. i) ; 



(2) the blowout is old or has ceased its development and part or all of 

 it has become stabilized by the action of plants (PI. XI, Fig. 2) ; or 



(3) two or more blowouts have grown together or smaller secondary 

 blowouts have begun within them, interfering with the regular ar- 

 rangement of the physiographic features and plant associations (PI. 

 IV, Fig. 2). Any two, or all three, of these may act together. Ob- 

 servation shows that stabilization may begin in any part of the blow- 

 out, whether it is young and small or large and old. When two or 

 more blowouts grow together, the most usual disturbance in their 

 regularity is the combination of the two deposits or the filling of 

 the basin of one by the deposits of the other. The larger the space 

 occupied by the blow-out complex, the smaller is the probability of 

 stabilization and the greater the amount of loose sand exposed to 

 the wind. The complex may then occupy several acres of ground and 

 be an actual menace to agriculture in the vicinity (PI. X, Fig-. 1). 

 When in this condition it is locally known as 'Svild sand." The 

 most notable complex in this respect is the waste known as the Devil's 

 X"eck, in the Havana area north of Topeka, where more than forty 

 acres of land is covered by shifting dunes, which have a maximum 

 height of probably 50 feet (15 m.). Blowouts may sometimes de- 

 velop on the west side of a hill, in which case the windward slope, 

 if any, is composed of one or two lateral slopes on the north and 

 south sides. The basin is relatively high and the bunch-grasses at 

 the windward end are removed by wind alone .and not by gravity. 

 Blowouts may also develop on the east side of a hill (PI. VII. Fig. i), 

 resulting- in a strongly developed windward slope, and in a lee slope 

 and deposit which may be actually lower than the basin. 



Attention must be called to the fact that the general effect of the 

 wind is to reduce the elevations and fill up the depressions of the 

 surface. The dunes themselves are initiated and pei-petuated by the 

 growth of plants upon their summits. This has been well de- 

 scribed by Cowles in his report on the dunes of Lake ^lichigan 

 (iSpp: 175-190.) Even the migrating or wandering dunes, although 

 carried forward by the wind, leave a trail of sand behind, which 

 would soon exhaust them if continued ver}'- far. In a some- 

 what similar way there is a limit to the size and depth of 

 the blowouts. At the maximum depth the wind is no longer 

 able to lift sand up the lee slope from the basin. If too wide. 



