86 



cum association as equivalent in habitat to the Illinois blowouts. 

 There are some species in common, but in the opinion of the present 

 writer there is not sufficient resemblance in habitat or flora between 

 the two to justify their classification in the same ecological g-roup. 



The only ecological discussion of the inland' region of Illinois is 

 by Gleason (Hart and Gleason, igoy: 162-167, 169-171). The 

 origin, growth, and stabilization of the blowouts of the Havana area 

 were discussed and the typical plants were listed. The different 

 physiographic parts of the blowouts, and their four plant associations 

 and the various successions between them were not recognized. 



In the normal development of a blowout, it probably always fol- 

 lows the Panicum pseudopuhesccns association, and consequently ap- 

 pears at the eastern side or in the center of that association. When 

 its development begins in the launch-grass association, without the 

 intervention of an intermediate society, it is probable that its inception 

 is due to some extraordinary local cause. The stamping of grazing 

 cattle has been suggested as a possible cause, and in one case a blow- 

 out started from a hole excavated in removing sand for building pur- 

 poses. 



If a single blowout can increase in size without coming in con- 

 tact with any others, it shows certain definite physiographic features 

 which appear to be constant. More often, however, several blowouts 

 originate near each other, and, becoming confluent with g^rowth, they 

 form a complex v/aste of sand (PI. IV, Fig-. 2) which baffles physio- 

 graphic analysis and sometimes causes the greatest difficulty in classi- 

 fying the meager vegetation. A complete typical blowout (PI. IV, Fig. 

 i)contains four parts, extending from west to east in the direction of 

 the prevailing winds. As a matter of fact the direction of the axis 

 of the blowouts may vaiy from north-south through west-east to 

 south-north. In the following discussion the direction is always 

 spoken of as west-east, for the sake of brevity. At the western end 

 there is a doAvnward slope from the g'eneral level, here tenned the 

 windward slope. From it sand is being removed by the wind toward 

 the east, and is also settling down by gravity toward the bottom of 

 the slope. The windward slope generally occupies a more or less 

 crescent-shaped area extending partly around the north and south sides 

 of the blowout. The deepest portion is termed the basin, and from 

 it sand is being rapidly carried away by the wind. Some is also 

 being deposited by wind and gravity from the windward slope, but 

 the resultant is in favor of the g-eneral removal of sand. A crescent- 

 shaped sloping area toward the eastern end of the blowout is termed 

 the lee slope. There the rates of erosion and deposition are about 



