McLOUTH ON DUST SHOWER. 173 



follows: Grand Ilaven, 26; Milwaukee, 12; Green Bay, 14; Chicago, 16. 

 These it must be understood were not maximum velocities but velocities 

 at moment of taking data for the daily report. At Grand Haven on this 

 date the maximum 1-minute record was 42 miles per hour at 9:17 a. m. 

 and the maximum 5-minute record was 37 miles per hour at noon. Quite 

 probably there was a similar rise in velocities above the morning records 

 at stations on the west side of Lake Michigan, and these strong winds 

 may have caught up the material in southern Wisconsin during the fore- 

 noon and swept it across the lake at 50 miles per hour in the upper cloud 

 regions. 



It is plain that the evidence I have been able to accumulate up to time 

 of writing is quite insufficient to make a satisfactory demonstration. At 

 first thought it seemed that only a spiral wind of tornado violence could 

 have lifted such a mass high in air where it could be sustained and carried 

 on air currents that probably did not exceed a velocity of 50 miles an 

 hour, but no disturbance of that nature is indicated in any of the weather 

 reports. The dust was raised and carried by winds that are frequently 

 exceeded in violence and equalled in constancy. It would seem therefore 

 that we should have about twenty dust showers each year rather than one 

 in about twenty years. 



Besides persons and institutions named before I am indebted to Mr. 

 Frank Leverett of the U. S. Geological Survey for important information 

 on extent of the loess, also to numerous correspondents through whom I 

 have been able to approximate the limits of the fall. 



Muskegon, March 26, 1902. 



