142 L. E. HICKS — SOME ELEMENTS OF LAND SCULPTURE. 



sharp edges. Indeed, this important factor occasionally seems, for the 

 time being, to be wholly wanting. Forms like figure 9 are not uncommon 

 in the bad lands. The summit b b is protected with turf and the water 

 curves b c extend to the very crest without a trace of a weather curve; 

 but the elimination of this factor is transitory. Visit the same butte 

 some years later and you will find, if water sculpture is still vigorous, 

 that the two water curves have so nearly joined that the turf has dis- 

 appeared and a short weather curve occupies the narrow crest, as in 

 figure 7 (Gilbert's figure 60), or, if water sculpture has been dormant, the 

 angles b b are replaced by weather curves. In a bad-land region all 

 stages of the process may be observed, from the level-topped sharp-angled 

 butte, often receiving the significant name " Box butte " or " Trunk butte," 

 shown in figure 9, to low domes like figure 5, which are not bad-land 

 forms at all. The same laws, the same processes are concerned in all 

 these varied results,'and a philosophic view of the subject demands that 



Figure 9.— Miniature Butte in tlie Bad Lands. 



all phases and stages of land sculpture be grouped comprehensively 

 instead of singling out a particular phase, though that maybe a striking 

 one. 



Water Carve of Deposition. — The water curve of erosion, having its sky- 

 ward face concave, is not the only vertical water curve. There is also 

 the curve of deposition, which is convex upward. Where a mountain 

 torrent debouches upon the plain, the debris carried or rolled along by it 

 spreads out in a mass which is fan-shaped in ground plan and conical in 

 elevation. 



Alluvial Cone. — Such a deposit is usually called an alluvial cone, but, 

 in view of its radial extension from the mouth of the gorge, Hilgard calls 

 it a debris fan. The cross-section presents a typical water curve of depo- 

 sition, convex upward. 



Flood-plains. — The flood plains of rivers, so far as they are built up by 

 sediment spreading laterally from the channel during floods* follow the 



* This is the usually accepted meaning of the term flood plain, namely, that it is the work of a 

 constructive river which is silting up its valley, or certain portions of it, during inundations. Gil- 

 bert uses the term in a very different sense. He says in Geology of the Henry Mountains, p. 132: 



"* * flood-plains are usually produced by lateral corrasion. There are instances, especially 

 neai' the seacoast, of river plains which have originated by the silting up of valleys, ami have been 

 afterward partially destroyed by the same rivers when some change of level permitted them to 



