0. R. Keyes — Eolian Origin of Loess. 301 



To the inhabitants of the region these dust-clouds often 

 become almost unbearable. Dust is everywhere. It sifts 

 through the closed windows and doors of the houses, cover- 

 ing everything within. Out-doors all is yellow with an impal- 

 pably fine powder. Man and beast suffer while the storm lasts. 



The north and east side of the river suffers more and oftener 

 than the south and west side. This is on account of the pre- 

 vailing winds coming from the southwest in the spring and 

 summer, when the silt bars are bare and dry. The north and 

 northwest winds are most frequent during the winter when 

 the ground is frozen or covered with snow. 



The length of the " dust storm " varies. It may last only a 

 single day, or it may continue through three or four days. 

 The total number of days out of the year during which the 

 dust clouds are driven with greater or less severity, is about 

 thirty. During five-sixths of this period, the wind blows 

 from the south and west. 



The observations here recorded were made chiefly at Jeffer- 

 son City during the years 1895-7. The measurements were 

 made at the State capitol, which is located on the very brink 

 of a high cliff, rising from the river's edge. The dust clouds 

 thus came directly off of the flood-plain below. Numerous 

 other notes were taken, but no accurate measurements made, 

 at other places along the Missouri, as at Omaha, St- Joseph, 

 Leavenworth, and Kansas City, and at St. Louis and elsewhere 

 on the Mississippi. 



The amount of dust brought up out of the valley at the 

 Missouri capital and deposited on the top of the bluff was, in 

 the several instances particularly noted, about one one- 

 hundredth inch in a day. An open book placed in a protected 

 nook was after a few hours so covered with dust that the print 

 could not be distinguished. For the period of 25 days this 

 would indicate a deposit of about one-quarter inch in a year, 

 which is probably not far from an average for the margin 

 nearest the river on the north side ; while on the south side of 

 the stream the total annual deposition would be very much 

 less. 



The amount deposited each day at auy one place depends to 



a large extent upon the relation of the direction of the wind 



and that of the stream valley, very much less silt dust being 



carried out when the direction of the wind is directly across 



the valley than when the two directions are at an angle. In the 



latter case when the bare silt areas are exposed to the full 



sweep of a strong breeze, the dust rises high in the air and is 



carried far inland. The observations already noted were made 



chiefly at the point where there was a direct sweep of about 



ten miles. The daily amount carried would be, therefore, 



Am. Jour. Sci.— Fourth Series, Yol. VI, No. 34.— October, 1898. 

 21 



