216 



EARTH FEATURES AND THEIR MEANING 



table mountain. Along its front, detached outliers usually stand 

 like sentinels before the larger mass, and according to their rela- 

 tive proportions, these are referred to either as small mesas or 

 as the smaller buttes (Fig. 228). 



-" >" : ; -^ 

 *'* 



FIG. 228. Mesa and outlying butte in the Leucite Hills of Wyoming (after Whit- 

 man Cross, U. S. G. S.). 



The war of dune and oasis. In every desert the deposits 

 are arranged in consecutive belts or zones which are alternately 

 the work of wind and water. Surrounding the desert and upon 

 the flanks of the mountain wall there is found (1) the deposit of 

 loess derived from the dugt that is carried out of the desert by 

 the wind. Immediately within the desert border at the base of 

 the mountains is (2) the zone of the dwindling river with its 

 sloping bench of coarse rubble and gravel. Next in order is 

 (3) the belt of the flying sand, a zone of dune ridges often sepa- 

 rated by narrow, flat-bottomed basins (Fig. 229) into which the 



FIG. 229. Flat-bottomed basin separating dunes bajir or takyr (after Ells- 

 worth Huntington). 



strongest streams bring the finer sands and silt from the moun- 

 tains. Lastly, there is (4) the central sink or sinks, into which 

 all water not at once absorbed within the zone of alluviation or 

 in the zone of dunes is finally collected. Here are the true lacus- 



