WIND DEPOSITS 687 



with strips of muslin suspended inside. These strips as well as the inner 

 surface of the cylinder were washed once a week and adhering particles 

 thus secured. Eight samples were taken b}^ this method during the 

 months of July, August, and September, in 1895. The cylinder was 

 suspended at the same height and from the' same flagpole as the broom- 

 corn and the muslin previously mentioned. In this series of samples 

 also there was a correspondence between the wind velocities and the 

 quantities of dust caught, though not so well marked as in the other 

 instances referred to. On the nineteenth of February, in 1896, when 

 there was a high wind and much dust in the atmosphere over the Mis- 

 sissippi Valley, one more sample was taken in the cylinder, this time 

 suspended only 10 feet above the ground. 



All dust caught in the cylinder, excepting two samples, is coarser than 

 that which was caught on adhesive surfaces. The maximum grade con- 

 sists of coarse dust in the former, while in the latter it is medium dust. 

 It appears that the slack wind was not retained in the cylinder long 

 enough to allow the fine particles to settle. In this way the maximum 

 has been transferred toward the coarse grades. It is to be inferred, also, 

 that the coarsest particles caught on the adhesive surfaces would more 

 frequently be rubbed and shaken off than the finest particles. 



List of Samples in Tahle 27 



286. Dust collected from the atmosphere in winds not exceeding 9 miles per 



hour. 



287. Dust collected from the atmosphere in winds not exceeding 10 miles per 



hour. 



288. Dust collected from the atmosphere in winds not exceeding 12 miles per 



hour. 



289. Dust collected from the atmosphere in winds not exceeding 13 miles an 



hour. 



290. Dust collected from the atmosphere in winds not exceeding 19 miles an 



hour. 



291. Dust collected from the atmosphere in winds not exceeding 22 miles per 



hour. 



292. Dust collected from the atmosphere in winds not exceeding 22 miles per 



hour. 



293. Dust collected 90 feet above ground in Rock Island, Illinois, June and 



July, 1895. 



294. Dust collected 10 feet above ground under trees, Rock Island, Illinois, 



September, 1895. 



295. Dust from top cloth on flagpole, August 19, 1895, Rock Island, Illinois. 



296. Dust from bottom cloth on flagpole, August 19, 1895, Rock Island, Illinois. 



297. Dust collected in a hollow cylinder 90 feet above the ground at Rock 



Island, Illinois, summer of 1895 ; maximum wind velocity, 14 miles per 

 hour. 



XLIX— Bull. Geol. Soc. Am., Vol. 25, 1913 



