174 



It is also a matter of record that the fires did destroy some of 

 the trees at or near the forest margin, and thus gradually drive 

 back the forest toward the east. The margin of the forest in 

 Illinois was originally characterized chiefly by hazel, a shrub 

 which is not seriously affected by repeated burning. Inside of 

 the hazel zone the forest was composed chiefly of oak, especially 

 Quercus velutina and Quercus imbricaria, neither of which pro- 

 duces a very dense shade. There seem to be no authentic data 

 on the matter, but it is entirely probable that even within the 

 hazel margin there were numerous grasses, sufficient to feed a 

 more destructive fire than the usual litter of leaves and dead 

 twigs. At the present time, at least, various prairie species 

 are found within the forest margin (1910, pp. 119, 123, 124)* and 

 their number and density is greatly increased by even a small 

 increase in the amount of light. The only undisturbed contact 

 of typical virgin prairie and forest observed by the writer in 

 Illinois has been so long protected from fire that the forest 

 margin has grown up to an almost impenetrable thicket of 

 several species of shrubs, whose prevailingly avevectent mode 

 of dispersal may indicate their recent arrival in the habitat. 



It has generally been the idea that prairie fires were vast 

 conflagrations, driven before the wind at an incredible rate, 

 and consuming everything in their path. Such fires doubtless 

 occurred, but the violent winds necessary for driving them are 

 not common in the Middle West in the early autumn, when the 

 fires were most abundant. When such fires did occur, they 

 naturally created a more vivid impression in the mind of the 

 observer, so they were chosen for printed description.! The 



* Henry Allan Gleason, The vegetation of the inland sand deposits of Illinois. 

 6 illustrations, 20 plates. Illinois State Laboratory of Natural History Bulletin, 

 vol. 9, pp. 23-174. Urbana, 1910. 



t An anonymous author describes a prairie fire in these words (Travels through 

 the United States and Canada, London, 1828, p. 187): "The flames advanced 

 very rapidly, continued to spread, and before they had arrived opposite to the 

 place where I stood, formed a blaze of fire nearly a mile in length. How shall I 

 describe the sublime spectacle that then presented itself? I have seen the old 

 Atlantic in his fury, a thunder storm in the Alps, and the cataracts of Niagara; 

 but nothing could be compared to what I saw at this moment. The line of flame 

 rushed through the long grass with tremendous violence, and a noise like thunder; 

 while over the fire there hovered a dense cloud of smoke. The wind, which even 



