IOWA ACADEMY OP SCIENCES. 
97 
principles. Our country is not too cold, neither is it too dry; 
the rainfall in eastern Iowa being almost, if not quite as great 
as in Indiana, where the primeval forest was once heaviest. 
Indeed the uniformity of general conditions raises the prob- 
lem: there seems to be nothing to hinder, therefore why is not 
the forest universal? 
Various answers have been given to this question.^ 
The opinion first entertained and that which is generally still 
current among common people, was that the continental forests 
were limited by fires. The Indians started fires and these fires 
were slowly, at the advent of the white man, consuming the 
woods, had stripped large areas in the Mississippi valley and 
unchecked would eventually have reached the Atlantic coast. 
No one who has been an eye-witness of the conflagrations that 
once rolled in annual tides across low^a or Illinois can doubt the 
force of the theory so long and so widely entertained. The 
difficulty lies in the fact that the forest stood the attack so well, 
in fact seemed largely unaffected, actually held its own in 
nearly every part of the fire -infested district. Then again, if 
the truth had been that the aborigines were destroying the 
woods at the time when the whites first became witnesses, proof 
of the fact should be found over the whole region in form of char 
red logs, stumps, etc., of which, needless to remark, there has 
been no trace whatever. The fire theory not v/holly satisfac- 
tory, some students went to the other extreme and urged that 
the distribution of the woods was due to causes efficient in 
times remotely past, so that fires or present conditions had 
nothing at all to do with the matter; the solution of the prob- 
lem must be sought in some earlier geologic age. Oohers 
again sought to solve the problem by a priori method. It was 
urged that trees exhaust the soil of one set of elements while 
grasses, herbaceous plants, demand something entirely differ- 
ent, so that either set of plants occupying for long ages a given 
region would exhaust its availability though leaving the ground 
serviceable for something else. Thus trees once occupied the 
whole Mississippi valley but had exhausted the ground of tree- 
material, so to speak, had worn out their welcome. The 
answer to this is that here in Iowa trees seem to grow every- 
where if planted and cared for. 
iSee inter al. Am. Journal of Science VI, 384; XXXVIII, 332 and 344; XXXIX, 317; 
XL, 23 and 293. Geol. Survey of Illinois I, 238 et seq; Geology of Iowa, Hall, I. Part I, 
p. 23 et seq; U. S. Geol. Survey, Eleventh Annual Report of the Director, p. 296 ct seq. 
