FOREST GEOGRAPHY AND ARCHOLOGY. 215 
the different views taken upon this knotty question. The only 
settled thing about it is, that the prairies are not directly due 
to a deficiency of rain. That the rain-charts settle, as Pro- 
fessor Whitney well insists. 
The prairies which indent or are inclosed in our Atlantic 
forest region, and the plains beyond this region, are different 
things. But as the one borders —and in Iowa and Nebraska 
passes into—the other, it may be supposed that common 
causes have influenced both together, perhaps more than Pro- 
fessor Whitney allows. 
He thinks that the extreme fineness and depth of the usual 
prairie soil will account for the absence of trees; and Mr. 
Lesquereux equally explains it by the nature of the soil, in a 
different way. These and other excellent observers scout the 
idea that immemorial burnings, in autumn and spring, have 
had any effect. Professor Shaler, from his observations in the 
border land of Kentucky, thinks that they have, — that there 
are indications there of comparatively recent conversion of 
Oak-openings into prairie, and now — since the burnings are 
over — of the reconversion of prairie into woodland. 
I am disposed, on general considerations, to think that the 
line of demarcation between our woods and our plains is not 
where it was drawn by Nature. Here, when no physical bar- 
rier is interposed between the ground that receives rain enough 
for forest and that which receives too little, there must be a 
debatable border, where comparatively slight causes will turn 
the scale either way. Difference in soil and difference in expo- 
sure will here tell decisively. And along this border, annual 
burnings — for the purpose of increasing and improving Buf- 
falo-feed — practised for hundreds of years by our nomade 
predecessors, may have had a very marked effect. I suspect that 
the irregular border line may have in this way:been rendered 
more irregular, and have been carried farther eastward wher- 
ever nature of soil or circumstances of exposure predisposed 
to it. 
It does not follow that trees would reoccupy the land when 
the operation that destroyed them, or kept them down, ceased. 
The established turf or other occupation of the soil, and the 
