662 POPULAR SCIENCE MONTHLY. 



for a general estimate, which is made here in the absence of a 

 better one. 



If we say that this western country experiences a dust storm 

 twice a year, we do not rate this work too high. During two such 

 days the velocity of the wind for the lowest mile in the atmos- 

 phere will average, at least, thirty miles an hour, and the total 

 wind movement will be 1,440 miles. Of course, there are many 

 sheltered places where such winds will not be felt. The territory 

 including the west two thirds of the Dakotas, of Nebraska, Kan- 

 sas, Oklahoma, and Texas, and extending west to the Pacific Ocean, 

 contains about 1,000,000 square miles of open land, allowing one 

 third the area for mountains. For the time of the storm the 

 atmosphere over this area may be regarded as a current of air 

 1,000 miles long, 1,000 miles wide, and a mile high, containing 

 1,000,000 cubic miles of air. If the lowest 200 feet in this current 

 carry a load of 20,000 tons to the cubic mile, and if the remain- 

 ing 5,080 feet carry 100 tons per cubic mile, there will be 853 tons 

 of dust to each square mile of the whole area of the current, 

 making a total of 853,700,000 tons transported a distance of 1,440 

 miles, or, if the expression be permitted, 1,229,342,400,000 mile- 

 tons of transportation will be performed. 



Comparing this with the quantity of work performed by the 

 water of the Mississippi drainage system, we find that the latter 

 is three hundred and thirty times as great. The Mississippi car- 

 ries annually 406,250,000,000 tons (estimate by Humphrey and 

 Abbott) of sediments a distance of, say, 1,000 miles, performing 

 406,250,000,000,000 mile-tons of transportation. The ratio of the 

 atmospheric transportation in the West and the aqueous trans- 

 portation in the Mississippi basin is then 1 : 330. 



If the above estimates have any significance at all, it is to the 

 effect that in this country the work of the atmosphere is less than 

 the work performed by meteoric waters. So far the inference is 

 in full accord with the well-grounded general consensus among 

 geologists. 



Care has been used to not overrate any of the factors entering 

 into the estimates. In sandy regions a considerable amount of 

 transportation is effected by pushing by the wind on the loose 

 surface material. This part of the work of the wind is here en- 

 tirely neglected. It is known, too, that even on calm days the at- 

 mosphere carries an appreciable load of dust, and this has not 

 been taken into account, though it operates for the remaining 

 three hundred and sixty-three days of the year. It is, therefore, 

 possible that the general estimate is too low. But it is not neces- 

 sary to have recourse to such a supposition alone to show that, 

 locally, work by the atmosphere may exceed the work performed 

 by the water. The observed average wind velocities in these 



