56 PRINCIPLES OF STRATIGRAPHY 



From this Free deduced the formula V = Kr, where K is a con- 

 stant for the conditions of experiment and r the radius of the 

 particle. 



From numerous measurements Udden concluded that the "aver- 

 age largest size of quartz particles that can be sustained in the air 

 by ordinary strong winds is about o.i mm. in diameter" (Udden- 

 97), but the largest particle that can be transported (not held in 

 suspension) is nearer 2 mm. in diameter', while gravel the size of 

 peas may in rare cases be carried along by the wind. This, how- 

 ever, represents the limit of ordinary deflation. (Walther-104 : 

 P7.) Much larger fragments, nevertheless, are rolled along by the 

 wind, and sometimes even lifted and carried for some distance. 

 Stones as large as a man's fist have been observed blown along by 

 wind in the deserts of Sahara (Rohlfs), and Gobi (Przhevalsky), 

 and Pumpelli saw stones 2 inches across blown by a storm in Tur- 

 kestan. (Pumpelli-77:joj.) A wind-blown pebble 2 cm. in di- 

 ameter was collected from the snows of Ben Nevis after a severe 

 storm. (Murray and Renard-69 : 590, also Theobold-93 : 55-^- 

 SS^.) A remarkable case is reported by St. Meunier (66a : 440; 73 : 

 24/'-248) of a "rain" of limestone pebbles, whose diameter ranged 

 from 25 to 35 mm., which fell on June 6, 1891, in the Department of 

 Aube, France. These pebbles are believed to have been transported 

 150 km. Other pebble falls are recorded by various observers. Or- 

 ganisms, often of some size, are also known among the remark- 

 able "solid" rains. Thus a fall of lichens was reported from Persia 

 by De Candolle. Falls of small live fish have been reported from 

 Madras, India, and were also observed at Singapore, in the Malay 

 peninsula; at Winter Park, Florida, in June, 1893; and at Tillers 

 Ferry, South Carolina, in 1901. A turtle 6 inches by 8 inches, and a 

 stone fragment ^ inch by ^ inch, both incased in ice, fell at Vicks- 

 burg, Mississippi, on May 11, 1894. (Abbe cited by Free-33.) 



Sokolow gives the following table of quartz sand grains moved 

 by varying wind velocities, as derived from his experiments 

 (87:72). 



Strength of wind in meters Maximum diameter of 



per second. sand grains per mm. 



4-5— 6.7 • 0.25 



6.7—8.4 0.5 



9.8 — 1 1. 4 1.0 



1 1. 4 — 13.0 1.5 



These results are only approximate. Sokolow holds that eolian 

 deposits with grains above 4 to 5 mm. in diameter are not known. 



