BARREN AND EDMONSON COUNTIES. 9 
_ The largest trees are oaks, about fifteen inches in diameter 
three feet from the ground. I saw scarcely a willow or a maple 
of any kind. The soil is a stiff limestone, considerably impreg- 
nated with iron, making it of a red color, and not highly pro- 
ductive of ordinary cereals. The surface is very uneven, being 
full of sinkholes, formed by the falling in of the cavernous 
passages which form a network under this whole district. The 
celebrated Mammoth Cave is only one of the hundreds of cav- 
erns of this remarkable region. Not in the trees only, but 
also in the herbaceous flora, was the limited number of spe- 
cies noticeable. It is well understood that the aborigines of 
this country were accustomed to burn over the surface of the 
prairies; but for what purpose it does not seem to be perfectly 
understood. There may have been several considerations 
which led them to this quite universal custom. It has been 
said that they thus destroyed the old culms of grass, and 
cleared the way for the springing of the tender shoots in the 
spring. They may also have had in view the destruction of 
hurtful insects, as the grasshoppers, by destroying their eggs, 
or of noxious serpents, which must have been destroyed in 
immense numbers by the annual fires on the prairies. Another 
reason may have had consideration; the tall dead grass would 
be liable to be fired by accident at any time, and thus human 
life and many villages be endangered in the night, or in times 
of high winds, with no means of escape; but if at a certain 
time, when all are on the lookout, the firing should take place, 
there would be no danger to life or property. 
This habit of firing the prairies must have exerted a wide 
influence on the character and distribution of plants in the 
parts of our country where prairies existed. Certain plants 
could not survive the fires. The annuals must have been 
greatly diminished by the custom. Those which were peren- 
nials under ground, would suffer less than any other class of 
plants. The fire swept off everything above the surface— 
seeds not covered by the soil, young plants of trees; but the 
well-protected living roots of herbaceous perennials, with the 
nourishment of another crop of shoots stored away safely be- 
35 
