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EROSION PERFORMED BY THE ATMOSPHERE.
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the experiment are of the most delicate kind and a slight change in the velocity will cause a considerable variation in the quantity of the load.

If then the ratio of the sections of the two currents is ⁠1/1000000⁠, the ratio of their velocities ⁠1/10⁠, and the ratio of their loads per unit of bulk of the two media is ⁠10000/1⁠, the ratio of their respective transporting powers is as the products of these fractions, or ⁠1/1000⁠. This is the same as to say, that if a cubic foot of air can hold in suspension ⁠1/10000⁠ of the quantity of fine dust held in the same way by the water in the Mississippi river, and if the velocity of the winds in the atmosphere is on the average not less than ten times as great as the rapidity of the current in the river, and if the area of a vertical section of the atmosphere over the valley is 1,000,000 times as large as the area of a cross section of the lower stream,—then the capacity of the atmosphere to transport dust is 1,000 times as great as that of the river.

Atmospheric currents being loaded, mostly, only to the extent of an insignificant fraction of their capacity, their sediments will be better sorted than deposits in water-currents, which are more often loaded to their full capacity.

It is evident that the greater the load carried by any current, the shorter is the average distance from particle to particle while in transport. This increases the chances for the particles to be affected by each others' movements through the medium and thus for coming together to form clusters. This process, which has been called flocculation, causes more rapid sedimentation; for such a cluster of particles will fall faster through the medium than will the separate grains of which it is composed. Flocculation takes place among particles of all sizes, and small particles which would otherwise be retained in the supporting medium, will easily settle when collected into these clusters. Sediments which have been formed under such circumstances will hence contain a proportionally greater quantity of fine material than if flocculation had not taken place. But flocculation increases with the quantity of the load, and since the load of the atmosphere is

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