SOILS, ETC. 133 



all kinds of rock, such as quartzite, friable sandstone, mag- 

 nesian limestone, common limestone, impure chalk, clay, 

 clayey, and sandy shales, &c. Southwestern Minnesota is 

 almost one continuous prairie upon the drift which rests 

 directly upon, not only the hard Sioux quartzite but also 

 directly upon the granite. 



Thus, whatever the origin of the prairies may have been, 

 we have the positive assurance that their present existence in 

 Iowa and its immediate vicinity is not due to the influence 

 of climate, the character or composition of the soil, nor to the 

 character of any of the underlying formations. It now 

 remains to say without the least hesitation, that the real cause 

 of the present existence of the prairies in Iowa is the preva- 

 lence of the annual fires. If these had been prevented fifty 

 years ago Iowa would now be a timbered instead of a prairie 

 State. 



Thus far we have stated facts and what are deemed to be 

 legitimate deductions from them. The following are offered 

 only as suggestions. We have no evidence to show or suggest 

 that any of the prairies ever had a growth of trees upon them ; 

 notwithstanding the fact that those at least of the eastern 

 part of the great prairie region will support an abundant 

 growth of trees after they are introduced, if protected from 

 the tires. There seems to be no good reason why we should 

 regard the forest as any more a natural or normal condition 

 of the surface than the prairies are. Indeed, it seems the 

 more natural inference that the occupation of the surface by 

 the forests has taken place by dispersion from original centres, 

 and that they encroached upon the unoccupied surface until 

 met and checked by the destructive power of the fires. 



Then arise questions like the following, not easily 

 answered, and for which no answers are at present proposed: 

 When was fire first introduced upon the prairies, and how ? 

 Could any but human agency have introduced annual fires 

 upon them ? If they could have been introduced only by the 

 agency of man why did the forests not occupy the prairies 

 before man came to introduce his fires, since we see their great 



