1<J8 MICHIGAN ACADEMY OF SCIENCE. 



A REMAKKABLE DUST SHOWER. 



BY C. D. MCLOUTH. 



On January 27 of the present year (1902) a shower of dust fell over a 

 wide area in Western Michigan. The dust was mingled with snow and 

 the mixture was commonly mentioned as yellow snow. The fall of the 

 dust continued during a considerable part of the afternoon, — three to- 

 seven hours according to observers at different stations. 



The fall occurred during the subsidence of the anticyclone following a 

 storm of great energy that crossed the continent during several days pre- 

 ceding. The storm moved from northern California southeastward ta 

 Kansas, thence curving northeastward to Lake Superior. During and 

 following this storm strong winds were prevalent over a wide region that 

 came under its influence, although the winds were not exceptionally high. 

 On the date of the dust fall and the preceding day the winds over the lakes 

 and Mississippi valley were westerly. 



Along the coast the dust is known to have fallen as far south as Hol- 

 land and at Hart northward, indicating an extreme width of at least sixty 

 miles. It is known to have extended inland to Sparta, about thirty miles 

 from the lake shore. The territory bounded by a line slightly outlying 

 these points is not less than 1,600 square miles in area. It appears that 

 the precipitation was somewhat variable in quantity at different places 

 and there are some indications that the amount was greater twenty to 

 thirty miles inland than at Muskegon. 



Naturally there were many speculations as to the real nature of the 

 phenomenon. The dust was variously mentioned in public print as (1) 

 local surface material, especially from the dunes along Lake Michigan^ 

 (2) Volcanic dust; (3) Meteoric matter; (4) Earthy material raised from 

 the surface beyond the lake. The first supposition was easily disproved 

 by microscopical measurements of the grains, which showed its extreme 

 fineness as compared with local soil particles. Moreover, the fall was 

 observed on Lake Michigan windward from the land. The presence of con- 

 siderable organic matter showed that it could not have come from a 

 volcano or from outer space. Dr. A. C. Lane, State Geologist, pronounced 

 the dust identical with the loess soil of the Mississippi and Missouri river 

 valleys. Mr. W. A. Orton of the National Bureau of Plant Industry called 

 it fine silt. Thus the problem was narrowed down to finding the exact 

 source of the material and how it could have been raised and transported 

 so great a distance under conditions that did not seem exceptional. 



Some attempts were made at collecting data from which an approximate 

 estimate of the total deposit could be formed. Snow containing the dust 

 was taken from measured spaces and the dry residue weighed with re- 

 sults as follows : 



