582 C. R. KEYES — RELATIVE EFFICIENCIES OF EROSIONAL PROCESSES 



cycle is in one respect even better supported than that of the normal wet 

 cycle, "for while the arid African plains are examples of old desert plains 

 now growing still older, it is difficult to point out any large peneplain 

 that still stands close to the baselevel with respect to which it was worn 

 down/^ 



The plains-forming tendencies of arid eolation has in the humid re- 

 gions its nearest counterpart in the snow-drifting effects during a winter 

 "blizzard." The high winds drive the hard, dry snow particles over the 

 exposed grounds, filling the cuts of the railways and highways, ravines 

 and gullies, hollows and low places. On the bleak hills and ridges the 

 frozen ground is swept bare, and is often left protruding above the snow- 

 field. In the arctic regions, where the snow is in the form of small, thick 

 needles, rather than in the shape of flakes, the general leveling phenom- 

 ena are even more pronounced. The manifest tendency in both cases is 

 to make of an irregular surface an even plain. Were it possible to extend 

 the "blizzard" a week or a month, or repeat it at short intervals for a 

 longer period, instead of a single day, the general planation effects might 

 soon be made more conspicuous, and even the eolian erosion of the hills 

 might soon appear appreciable. 



In the desert region there are the same strong winds and the same dry 

 particles, only the latter are of soil instead of ice. Both process and ma- 

 terial are at hand the year around. Artificial excavations are quickly 

 smoothed over. The great systems of wing dams, or V-shaped ditches 

 and embankments, which some of the desert railways have had constructed 

 along the tracks to protect them against the effects of the cloud-burst 

 and the resulting "wash-outs," are, as I have noted, soon leveled again by 

 the driven soils.^^ 



In exposed places in the desert the railway has also often erected series 

 of high board fences as a protection against the drifting soils, after the 

 fashion of the northern railways in winter to curb the drifting snows. 

 At San Antonio, in the Kio Grande Yalley, the loose, mobile sands and 

 soils from off the Jornada del Muerto are, for distances of many miles, 

 swept into the basin, forming drifts hundreds of feet in thickness, until 

 they are finally carried away by the waters of the great stream. At San 

 Acacia, 50 miles to the northward in the same valley, similar prodigious 

 sand drifts occur. Many other places might be mentioned in the region 

 where like phenomena appear. The Libyan and Nubian deserts encroach 

 on the valley of the Nile in like manner. Only on a much larger scale, 

 such phenomena are not unlike the drifting sands of a seashore. 



35 Bulletin of the Geological Society of America, vol. 19, 1908, p. 80. 



