322 THE JOURNAL OF GEOLOGY. 



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 trans- 

 ported 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 transportatiofi by the atmosphere , rock materials 

 must be finely comminuted, the average largest size of quartz particles 

 that can be sustai?ied i7i 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 cor- 

 ners 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 : 



