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of the atmospheric ocean, throwing them upwards sometimes over 10,000 feet. Small quantities of incombustible matter are raised to the horizon of translation above by heated currents of air from chimneys and fires, and perhaps still smaller quantities by birds and other animals of flight.

Aside from these instances there are no important means by which the atmosphere is loaded, and for this reason, among others, its importance as a geological agent is small. The load to be carried must be raised before it is borne away. In water the contrary is almost always the case. The material to be transported is supplied at the water's surface and from the start to the end of the transport the sediments are allowed to slowly sink. They are transported forward and downward; in the atmosphere they must be transported first upward, and then forward.

To be subject to transportation by the atmosphere, rock materials must be finely comminuted, the average size of quartz particles that can be sustained in the air by ordinary strong winds being about .1 mm. in diameter.

This statement is based on a number of measurements, which have been made on sand and dust transported by the air. Among these are measurements of dust and sand raised by the wind from roads and streets in dry weather; of dust which fell on the ground at Kansas City, Mo., after a severe west wind on the plains; of dust collected after dry storms on the window-sills in residences in the central part of Kansas; of sand taken in crevices and corners in railroad cars in various parts of the country. It agrees with measurements made on volcanic dust known to have been carried several hundred miles in the atmosphere. Corroborating results have also been obtained by some simple experiments. The constituent materials of a coarse loam were separated into groups of different grades of fineness. These separations were thrown into the air and observations made on their behavior. The velocity of the wind was about eight miles per hour, and the observations may be tabulated as follows: