SCENERY, SOIL AND THE ATMOSPHERE 575 



us a group of results, not perhaps so nearly universal, but even more 

 tangible and conspicuous. Many agents are at work producing mineral 

 materials of such fineness that the winds can carry them. Oriental 

 travelers and explorers know the sand storm as one of the most dis- 

 tressing and sometimes deadly visitations. In the desert mechanical 

 disruption of rocks goes on rapidly and there is little moisture or plant 

 life to hold the fragments down. The winds become factors of trans- 

 portation in a manner little known by dwellers in moist and verdant 

 lands. Dust storms are not confined to the Sahara, or Persia, or Tur- 

 kestan. They occur in considerable numbers in our arid regions, where 

 they sweep for hundreds of miles, last for many hours and carry in- 

 credible loads. Sand drifts a foot high have gathered in a half hour 

 on railway tracks; thirteen cars of sand were taken from a single depot 

 platform in Colorado; the same careful student who reports these facts 

 estimates from 160 to 126,000 tons of sand carried in a cubic mile of 

 air. This for a single storm may give us hundreds of millions of tons 

 borne for hundreds of miles. Under such conditions the redistribution 

 of surface materials by the atmosphere can no longer be held trivial. 



We are now to remember that desert conditions furnish but a minor 

 part of the dust that is available. Wherever in all geologic time there 

 have been explosive volcanic eruptions, dust has been expelled, often in 

 prodigious amounts, covering leagues of sea with floating pumice, litter- 

 ing the decks of vessels hundreds of miles away, destroying crops, 

 darkening the atmosphere across wide seas, and enriching the sunset 

 glows, it is believed, around the globe. Every rain storm purges the 

 air of dust, much of local origin, no doubt, but some from remote and 

 subterranean sources. Here is ceaseless accretion for all land surfaces 

 and for all sea bottoms, and we have an impressive illustration of the 

 interdependence and the cosmopolitan efficiency of every part of the 

 earth's machinery. 



Man never uncovers a soil surface with the plow or by the passage 

 of hoof or vehicle, without exposing material to atmospheric migration, 

 and it is some years since an expert road maker, in a highway conven- 

 tion, set forth the havoc wrought on macadam roads by winds. 



From the point of view of natural scenery the winds' most con- 

 spicuous product is the dune. Many have seen a single example of a 

 belt or field of sand hills, but the student of the earth finds in them no 

 phenomenon of small range. He looks for them on the lee side of every 

 river in a desert region and along all sand shores. He finds them 

 invading the olive orchards of Palestine, the vineyards of France, the 

 meadows of Holland, the forests of the Great Lakes and the fields of 

 Cape Cod. The hand of man is put forth to stay the ravages of these 

 flying cohorts and the organized skill of a government department joins 

 in the task. Search is made for sand-binding grasses, in the same 



