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age velocity of the wind increases very fast and apparently not according to any definite law upwards for the first fifteen feet above the ground. Above this height it increases as the bisected chords of parabolas having their vertices in a horizontal line 72 feet below the surface. The parameters of these parabolas increase directly in the ratio of the squares of the velocities of the different winds. With a velocity of ten miles per hour at an elevation of fifty feet above the ground there will then be a velocity of about one hundred miles per hour one mile above the ground, but of less than one mile per hour near the surface. Observations made on the movements of clouds verify these calculations as to high velocities some distance up in the atmosphere. Whatever is to be transported any great distance must be lifted up to some considerable height above the surface of the earth, where the winds attain high velocities.

Over level plains, under ordinary circumstances, the conditions seem to be unfavorable for effecting any such upward transference, and little or no removal of material is apt to take place. But when a strong wind runs up against a vertical cliff, such as are seen in the bad lands or in the country of the plateaus and "mesas," eddies are no doubt set up which rise high above these vertical reliefs. A short valley or a reëntrant excavation in such a cliff will gather the wind and start it with increased force obliquely upwards, as it enters from the open end. In such a mobile element as the atmosphere an eddy like this may rise a considerable distance. No less effective in this respect are the whirlwinds in arid regions, which have been described by nearly every traveler in such countries.^[1] During the warm part of the day these can be seen, it is said, at almost any time in some direction of the horizon. They often rise to a great height, carrying with them the loose materials of the desiccated soil and giving them up to the incessant and steady run of the winds above.

The explosive outburst of a volcano similarly launches enormous quantities of minute fragments of pumice on the currents