132 PHYSICAL GEOGEAPHY. 



was not due to any unfavorable condition of climate. More 

 especial reference has here been made to the natural growth 

 and encroachment upon the prairies of the forest trees, bnt it 

 is proper to state here that the planting of these trees has 

 become a recognized branch of the agriculture of the State, 

 and every Iowa farmer knows that he may plant and grow a 

 crop of wood with the same certainty that he can grow a crop 

 of corn. 



4. ORIGIN OF THE PRAIRIES. 



The question of the origin of the prairies has become more 

 hackneyed perhaps, than any other of the speculative ques- 

 tions which North American geology affords; and yet it 

 seems to be no nearer a solution, satisfactory to all, than 

 it was when it first began to be discussed. It is not now 

 proposed to discuss this question at length, nor even to 

 present the different views that have been published by 

 different authors, but only to state a few facts, offer a few 

 suggestions, and perhaps leave the subject as unsettled in the 

 minds of others as it was before. 



By the word prairie we mean any considerable surface that 

 is free from forest trees and shrubbery, and which is covered 

 more or less thickly with grass and annual plants. This is 

 also the popular understanding of the term. It is estimated 

 that about seven-eighths of the surface of Iowa is prairie or 

 was so when the State was first settled. They are not confined 

 to the level surfaces, but are sometimes even quite hilly and 

 broken; and it has just been shown that they are not 

 confined to any particular variety of soil, for they prevail 

 equally upon Alluvial, Drift, and Lacustral soils. Indeed, 

 we sometimes find a single prairie whose surface includes all 

 these varieties, portions of which may be respectively sandy, 

 gravelly, clayey, or loamy. Neither are they confined to the 

 region of, nor does their character seem at all dependent upon 

 the formations which underlie them, for within the State of 

 Iowa they rest upon all formations, from those of Azoic 

 to those of Cretaceous age inclusive, which embrace almost 



