134 PHYSICAL OEOGEAPHY. 



tendency to encroach upon the prairies as soon as the tires 

 are made to cease ? The prairies, doubtless, existed as such 

 almost immediately after the close of the Glacial epoch. 

 Did man then exist and possess the use of fire that he might 

 have annually burnt the prairies of so large a part of the 

 continent, and thus have constantly prevented the encroach- 

 ment of the forests ? It may be that these questions will 

 never be satisfactorily answered ; but nothing is more evident 

 than that the forests would soon occupy a very large propor- 

 tion of the prairie region of North America if the prairie 

 fires were made to cease, and no artificial efforts were made to 

 prevent their growth and encroachment. 



5. FOREST TREES. 



Although the subject of the growth of wood is not, strictly 

 speaking, a geological one, yet it is proper to consider it in 

 this report in addition to coal and peat, as a part of the fuel 

 resources of the State; and it is introduced here as having 

 also a natural connection with the subjects discussed in the 

 pages immediately preceding. 



Wood is, and always has been, the principal and preferred 

 fuel of the inhabitants of the State for domestic use, and were 

 it everywhere in sufficient quantity, they would probably 

 never care to change their established habits in the use of 

 fuel by discarding it for any other. It has been feared by 

 many, that the amount of fuel which Iowa could be made to 

 produce ; would not be sufficient to meet the wants of the 

 prospective inhabitants that her fertile soil is capable of 

 supporting in plenty ; but it is believed that an examination 

 of the subsequent pages upon the subjects of coal and peat, 

 will show the groundlessness of such fears, even if no other 

 sources of supply are considered. In addition to that, it is 

 proposed to show in this place that a sufficient amount of 

 fuel, at least for domestic use, for all the present and pro- 

 spective inhabitants of the State may be produced from the 

 soil alone by the growth of forest trees. 



It has before been stated that forest trees can be cultivated 



